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CONDENSATION  OF  VAPOR  AS 
INDUCED  BY  NUCLEI  AND  IONS 


By  CARL  BARUS 

Hazard  Professor  of  Physics,  Brown  University 


WASHINGTON,  D.  C: 

Published  by  the  Carnegie  Institution  of  Washington 

May,  1907 


LIBRAJTST 

VNIVERSITY  OF  CALIFORNIA 

•nAVTQ 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
Publication  No.  62 


PREFACE. 


The  chief  purpose  of  the  present  volume  is  the  development  of  a  fog 
chamber  of  simplest  practical  character,  capacious  enough  to  admit  of 
the  measurement  of  the  largest  available  coronas,  and  efficient  up  to 
the  highest  exhaustions  applicable;  i.e.,  those  which  do  not  uselessly 
overstep  the  optical  limits  of  the  experiment,  where  fog  particles  become 
so  fine  as  to  be  virtually  inactive  in  diffracting  or  scattering  white  light. 
This  I  think  has  been  accomplished,  and  the  results,  as  far  as  they  go, 
seem  to  indicate  an  efficiency  not  inferior  to  Wilson's  piston  apparatus. 
I  have  not,  however,  been  able  to  get  much  beyond  the  large  green- 
blue-purple  corona,  no  matter  whether  the  nuclei  selected  were  effec- 
tively large,  like  the  ions,  or  effectively  small,  like  the  colloidal  nuclei. 
The  forms  beyond  are  flimsy  and  so  nearly  colorless  as  to  be  useless 
for  measurement;  but  the  steam-jet  nevertheless  reveals  a  whole  order 
of  axial  oranges  and  yellows,  lying  beyond,  which  to  my  knowledge  have 
not  been  detected  in  any  form  of  fog  chamber  whatever. 

As  used  in  most  experiments,  including  my  own  earlier  work,  the  fog 
chamber  with  a  plug  stopcock  seems  to  be  of  very  inferior  efficiency 
in  comparison  with  the  piston  form.  This,  however,  in  a  properly  de- 
signed apparatus,  is  the  case  only  when  the  attempt  is  made  to  obtain 
the  isothermal  drop  in  pressure  observationally  at  the  fog  chamber, 
closed  at  once  after  exhaustion.  The  datum  needed  can  only  be  found 
by  computation,  and  the  initial  pressures  in  the  fog  and  vacuum  chambers 
and  their  final  pressure  when  in  contact,  always  at  the  same  temperature, 
suffice  for  this  purpose.  Though  I  was  prepared  for  some  corrections, 
I  did  not  anticipate  so  large  a  difference  between  the  apparent  drop 
and  the  true  drop  of  pressure,  as  actually  appears.  In  the  experiments 
which  follow,  the  ratio  is  in  fact  as  i,oco  to  775,  a  difference  of  nearly 
25  per  cent.  Hence  it  will  be  necessary  to  restandardize  the  coronas 
with  this  result  in  view,  an  undertaking  which  I  hope  to  begin  in  the 
near  future.  Indeed  a  large  number  of  incidental  results  would  have 
made  this  desirable  in  the  interest  of  other  investigations.  For  similar 
reasons  I  have  (as  a  rule)  continued  to  refer  the  nucleations  of  the  present 
volume  to  the  drop  in  pressure  observed  at  the  fog  chamber;  and  such 
reference  is  sufficient  for  the  comparisons  aimed  at,  if  the  same  type  of 
apparatus  is  used  throughout,  as  was  the  case. 

Having  improved  the  fog  chamber  to  the  degree  shown  in  Chapters 
I  and  II,  it  was  made  use  of  in  Chapter  III  for  certain  incidental  experi- 

iii 


IV  PREFACE. 

ments.  I  have  already  shown  in  case  of  dust-free  air  and  the  persistent 
nuclei  produced  by  intense  X-radiation  that  the  distribution  of  nuclei 
within  the  fog  chamber  is  a  most  remarkable  feature  of  the  experi- 
ment. The  same,  however,  is  true  of  the  ions.  Whether  produced  by 
X-rays  acting  from  long  distances  or  by  radium,  the  density  of  ioniza- 
tion is  as  a  rule  very  different  in  different  parts  of  the  fog  chamber, 
showing  the  important  effects  due  to  the  presence  of  secondary  radiation 
within.  Again,  the  change  of  nucleation  produced  when  the  exciting 
cause  (X-ray  bulb  or  radium  tube)  is  removed  at  different  distances 
from  the  fog  chamber  was  to  be  reinvestigated.  Associated  with  this 
experiment  is  the  occurrence  of  minima  of  nucleation  for  certain  dis- 
tances, supposing  the  exhaustion  to  be  sufficiently  high  to  induce  con- 
densation of  ions  and  colloidal  nuclei  in  presence  of  each  other.  Finally, 
if  the  rate  of  decay  of  ions  can  be  inferred  from  independent  electrical 
experiments,  a  method  for  the  standardization  of  coronas  is  presented 
which  bids  fair  to  be  the  most  satisfactory  solution  of  the  problem 
suggested.  The  method  admits  of  a  determination  not  only  of  the  rela- 
tion of  the  nuclei  corresponding,  in  a  given  case,  to  two  different  coronas 
(cat.  par.),  but  of  the  absolute  nucleation  involved.  There  is  also  a 
possibility  of  detecting  in  this  way  how  a  given  mass  of  precipitated 
water  is  distributed  among  nuclei  of  different  sizes  when  occurring 
together — one  of  the  most  important  of  the  problems  outstanding  in 
connection  with  this  apparatus. 

Chapter  IV  adduces  a  variety  of  results  for  colloidal  nuclei  in  media 
other  than  air- water.  It  is  shown,  for  instance,  that  there  is  no  evidence 
to  prove  the  colloidal  nuclei  in  a  medium  of  carbon  dioxide  and  water 
are  larger  than  in  the  normal  case  of  air  and  water,  in  spite  of  the 
presence  of  the  coercible  gas  in  which  groups  of  larger  molecular  aggre- 
gates would  be  anticipated.  On  the  other  hand  relatively  large  colloidal 
nuclei  do  seem  to  occur  in  a  medium  of  air  and  alcohol  vapor.  Thus 
it  is  suggested  that  colloidal  nuclei  in  dust-free  wet  air  are  to  be  associated 
with  the  saturated  vapor  and  that  the  gas  is  only  secondarily  involved. 

In  Chapter  V,  undertaken  by  Miss  L.  B.  Joslin  under  my  direction,  a 
systematic  comparison  is  worked  out  of  the  relations  between  the  num- 
ber of  ions  in  the  atmosphere  and  the  corresponding  dust  contents  in 
the  lapse  of  time.  No  direct  connection  is  apparent,  whence  it  follows 
that  as  the  nucleation  is  largely  of  local  origin,  other  sources  must  be 
looked  to  for  the  ionization,  or  that  the  enormous  local  output  of  ions 
from  an  industrial  community  vanishes  so  rapidly  as  to  be  quite  negli- 
gible. On  the  other  hand,  it  may  be  possible  to  detect  evidences  of 
"absorption"  in  the  curves  obtained.  Incidentally  the  nucleation  of 
the  atmosphere  of  Providence  during  nearly  four  years  is  exhibited. 


PREFACE.  V 

Finally,  in  Chapter  VI,  I  return  to  the  problem  begun  in  Chapter  I, 
to  see  whether  there  is  any  change  in  the  colloidal  nucleation  of  dust- 
free  air,  such  as  might  be  ascribed  to  the  ionization  produced  by  some 
penetrating  cosmical  radiations  coming  from  without;  for  it  was  to 
be  the  plan  of  these  researches  to  study  the  ordinary  dust  content  of 
the  atmosphere  with  regard  to  its  variation  in  the  lapse  of  time  first,  and 
thereafter  to  continue  in  the  same  way  with  the  nucleation  of  the  dust- 
free  atmosphere.  This  nucleation  is  found  to  increase  synchronously 
with  the  decrement  of  the  barometer;  but  as  the  amount  of  adiabatic 
cooling,  i.  e.,  the  efficiency  of  the  apparatus  {ccet.  par.),  follows  the  same 
conditions,  it  is  extremely  difficult  to  disentangle  the  two  effects.  Never- 
theless the  results  are  of  considerable  interest  and  they  are  therefore 
reported  in  their  present  state  of  progress. 

My  thanks  are  due  to  Miss  L.  B.  Joslin,  who  not  only  gave  efficient 
assistance  in  the  preparation  of  the  manuscript  and  of  the  drawings  for 
the  press,  but  contributed  much  of  the  work  in  Chapter  III,  section  62, 
and  Chapter  V. 

Carl  Barus. 


CONTENTS, 


Chapter  I. — Early  Successive  Stages  of  Efficiency  of  the  Fog  Chamber  and 

Allied  Results. 

DISTRIBUTION   OF   NUCLEI    WITHIN   THE  FOG   CHAMBER   ENERGIZED    BY    THE 
GAMMA-RAYS  OF  RADIUM,  AND  BY  THE  X-RAYS. 

Page, 

i .  Introductory i 

2.  Data 3 

3.  Explanation 5 

4.  Further  experiments  with  radium.     High  exhaustions 5 

5.  The  same,  continued.      X-rays 6 

6.  The  same,  continued.      Miscellaneous  tests , 7 

7.  Distance  effects  of  radium 9 

8.  Cause  of  the  minimum  and  the  maximum 10 

9.  Further  experiments  with  radium 12 

10.  Distance  effect  of  penetrating  X-radiation 12 

1 1 .  General  inferences  (radiant  fields) 13 

THE    NUCLEATION    OF    FILTERED    AIR    IN  RELATION  TO  DIFFERENT  SUPER- 
SATURATIONS  OF   WATER   VAPOR. 

1 2.  Successive  series  of  results 13 

13.  Effect  of  X-rays  and  gamma-rays.     Data 18 

14.  Persistent  nuclei 18 

15.  Persistent  nuclei  generated  through  tin  plate 20 

16.  Discussion 21 

17.  More  rapid  exhaustion.     Apparatus  and  data 23 

18.  Remarks  on  the  j-curves.     Non-energized  air 25 

19.  The  same,  continued 26 

20.  The  same,  continued.     Action  of  radium 27 

II.  The  same,  continued.     Action  of  X-rays 27 

22.  Remarks  on  the  n-curves.     Non-energized  air 27 

23.  The  same.     Action  of  radium 29 

24.  The  same.     Action  of  X-rays 29 

25.  Remarks  on  the  iV-curves 29 

THE   NUCLEATION   OF   FILTERED   AIR   IN   THE   LAPSE   OF  TIME. 

26.  Method 30 

27.  Early  data 30 

28.  Apparatus  modified 31 

29.  Inferences 31 

SUMMARY   OF  THE   RESULTS   OF   THE   CHAPTER. 

30.  Distribution  of  ions  within  the  fog  chamber 32 

31 .  Minimum  of  efficient  nucleation '. 32 

32.  Persistent  nuclei 32 

33.  Dependence  of  efficiency  of  fog  chamber  on  the  size  of  the  exhaust  pipes. ...  33 

34.  Invariable  character  of  colloidal  nucleation  in  the  lapse  of  time 33 

VII 


VIII 


CONTENTS. 


Chapter  II.—  Later  and  Final  Stages  in  the  Efficiency  of  the  Fog  Cham- 
ber due  to  a  Gradual  Increase  in  the  Bore  of  the  Exhaust  Pipes. 

CONNECTING   PIPES   NOT  LARGER  THAN   1. 5   INCHES   IN   DIAMETER. 

Page. 

35.  Introductory 34 

36.  Examples  of  data  for  i-inch  connecting  pipes 35 

37.  Data  for  pipes  1 J  inches  in  diameter 35 

38.  The  same,  continued.     Shorter  pipes 38 

CONNECTING   PIPES   2    INCHES   IN   DIAMETER. 

39.  Remarks  on  the  method 41 

40.  Data  for  pipes  2  inches  in  diameter,  1 2  inches  long 42 

41.  The  same,  continued.     X-ray  bulb  inclosed  in  lead 44 

42.  Discussion 45 

43.  Radiant  fields 49 

COLLOIDAL     NUCLEI     IN    DUST-FREE   AIR.       EXHAUSTION    PIPES    AND    STOP- 
COCKS  4   INCHES  IN  DIAMETER. 

44.  Purpose 5 ! 

45.  Apparatus 5 1 

46.  Exhaustion  difficulties 53 

47.  Same,  continued.     Case  of  air  in  fog  chamber  saturated  with  water  vapor.  .  .  55 

48.  Case  of  saturated  air  in  both  chambers 59 

49.  Observations  with  4-inch  exhaust  pipes 65 

50.  Observations,  continued 70 

5 1 .  The  same,  continued 71 

52.  Discussion 73 

53.  Summary 73 

Chapter  III. — Miscellaneous  Experiments. 

54.  Objects 77 

55.  Growth  of  persistent  nuclei 77 

56.  Water  nuclei  produced  by  evaporation 78 

57.  Distance  effects.     X-rays 82 

58.  The  same,  continued.     Small  wood  fog  chamber 85 

59.  The  same,  continued.     Large  wood  fog  chamber 85 

60.  The  same,  continued.     Discussion 86 

61.  Distance  effect  and  absorption.     Radium 89 

62.  Falling  to  pieces  of  ions  in  the  lapse  of  time 91 

63.  Decay  curve 95 

64.  The  same,  continued 97 

65.  Condensation  phenomena  of  the  inclosed  steam  jet.     Methods  and  results ..  .  98 

66.  Summary 102 

Chapter  IV. — Distribution    of  Colloidal  Nuclei   and    of  Ions  in  Media 
other  than  Air-water. 

COLLOIDAL  NUCLEI  AND  IONS  IN  WET  DUST-FREE  CARBON  DIOXIDE  AND  IN 

WET  COAL-GAS. 

67.  Apparatus IQ5 

68.  Data  for  carbon  dioxide IQ5 

69.  Behavior  of  carbon  dioxide I07 

70.  Cause  of  differences IOj 


CONTENTS.  IX 

Page. 

71.  Nucleation  increases  subject  to  a  uniform  law  of  equilibrium 109 

72.  Data  for  coal  gas no 

73.  Character  of  the  early  results  for  coal  gas no 

74.  New  data  for  coal  gas in 

75.  Conclusion 112 

COLLOIDAL  NUCLEI    AND  IONS  IN  DUST-FREE  AIR  SATURATED  WITH  ALCOHOL 

VAPOR. 

76.  Introductory 112 

77.  Apparatus  and  method 113 

78.  Properties  of  alcohol  fog 113 

79.  Number  of  particles 113 

80.  Size  of  the  nuclei 115 

81.  Data  for  alcohol  vapor 1 18 

ABSENCE   OE  COLLOIDAL   NUCLEI   IN   STRONG   ODORS. 

82.  Introductory 120 

83.  Data  for  camphor,  turpentine,  naphthalene 120 

84.  Summary 121 

Chapter  V. — The  Cotemporaneous  Variations  0}  the  Nucleation  and  the  Ion- 
ization 0}  the  Atmosphere  0}  Providence.     By  Lulu  B.  Joslin. 

85.  Introduction 123 

86.  Measurements  of  nucleation 124 

87.  Data  for  nucleation 125 

88.  Remarks  on  the  table  of  nucleation 125 

89.  Mean  daily  nucleation  125 

90.  Mean  monthly  nucleations , 141 

9 1 .  Measurement  of  ionization 141 

92.  Data  for  ionization 143 

93.  Remarks  on  the  tables 149 

94.  Errors  of  measurement 150 

95.  Mean  daily  ionization 152 

96.  Mean  monthly  ionizations  and  conclusion 153 

Chapter  VI. — The    Variations  of  the  Colloidal  Nucleation  of  Dust-Free 
Air  in  the  Lapse  of  Time. 

97.  Introductory 155 

98.  Method  and  data 155 

99.  Deductions 157 

100.  Effect  of  the  barometer 158 

101.  Corrections 159 

102.  Further  data 160 

103.  Conclusion 164 


CHAPTER  I 

EARLY  SUCCESSIVE  STAGES  OF  THE  EFFICIENCY  OF  THE  FOG  CHAMBER 

AND  ALLIED  RESULTS. 

Before  beginning  the  main  subject  of  this  chapter  (see  section  2),  it 
is  advisable  to  add  a  few  measurements  of  the  distributions  of  ions  pro- 
duced within  the  fog  chamber  by  the  X-rays  or  by  radium  acting  from 
without,  since  these  occurrences  must  be  kept  in  mind  throughout  the 
measurements.  Again,  the  effect  of  different  classes  of  nuclei  (persistent 
nuclei,  ions,  and  colloidal  nuclei)  in  presence  of  each  other  is  similarly 
important  and  direct  light  must  be  thrown  upon  it  preliminarily. 

Under  all  conditions  the  fog  chamber  is  attached  to  a  large  vacuum 
chamber  by  a  rigid  passage-way  of  the  length  and  diameter  specified,  the 
ratio  of  the  volumes  of  the  two  chambers  being  about  as  6  to  100,  respec- 
tively. Moreover,  it  was  customary  to  read  off  the  drop  of  pressure  (dp) 
at  the  fog  chamber  (isolated  immediately  after  exhaustion  from  the 
vacuum  chamber)  when  isothermal  conditions  had  been  reestablished. 
The  observed  datum  suffices  for  the  comparisons  of  nucleation  when  the 
same  chambers  are  used  throughout;  but  it  will  be  shown  in  Chapter  II 
that  it  is  much  in  excess  of  the  true  drop  of  pressure  and  that  the  latter 
is  to  be  computed  from  the  initial  pressures  in  fog  and  vacuum  chambers 
and  the  final  pressure  when  both  are  in  contact,  all  under  isothermal 
conditions. 

After  completing  the  work  of  section  2  of  this  chapter,  a  few  appli- 
cations were  made  with  the  apparatus  in  its  state  of  partial  completion 
for  the  purpose  of  ascertaining  whether  there  is  any  discernible  change 
of  colloidal  nucleation  and  by  implication  of  ionization  in  the  stagnant 
air  within  the  scope  of  the  method.  Several  months  of  observation 
showed  none.  The  early  data  have  been  added  to  the  chapter  for 
convenience  in  chronology,  though  they  slightly  interrupt  the  continuity 
of  the  research.  The  question  of  time  variation  is  taken  up  again  by  a 
different  method  in  Chapter  VI. 

DISTRIBUTION  OF  NUCLEI  WITHIN  THE  GLASS  FOG  CHAMBER,  WHEN 
THE  AIR  IS  ENERGIZED  BY  THE  GAMMA-RAYS  OR  THE  X-RAYS. 

1.  Introductory. — I  may  recall  at  the  outset  that  there  are  three 
classes  of  nuclei  to  be  considered  in  this  chapter,  the  first  of  which 
includes  the  ordinary  dust-like  or  persistent  kind.     They  may  be  sepa- 

1 


2  VAPOR    NUCLEI    AND    IONS. 

rated  from  the  air  by  the  filter  and  they  require  the  smallest  degree  of 
supersaturation  of  water  vapor  to  precipitate  condensation.  They  are 
usually  but  not  always  (necessarily)  foreign  bodies  in  the  air;  at  least 
they  are  producible  in  dust-free  air  by  the  X-rays  of  sufficient  intensity 
and  by  other  radiation.  The  second  class  comprises  the  fleeting  nuclei. 
They  are  often  charged  and  then  called  ions.  They  persist  for  very 
short  periods  of  time,  usually  vanishing  within  a  minute.  They  can 
be  maintained,  therefore,  only  in  the  presence  of  radiation,  corpuscular 
or  undulatory,  from  which  their  intimate  association  with  electrification 
or  with  ultra-violet  light  is  manifest.  Such  radiation  may  occur  spon- 
taneously within  the  body  of  a  gas  during  the  state  of  generation.  The 
sizes  of  these  nuclei  are  intermediate  between  the  first  or  dust-like  class 
and  the  third  class.  This  comprises  the  colloidal  nuclei  of  dust-free  air, 
which  are  virtually  persistent,  inasmuch  as  they  are  a  structural  part  of 
the  body  of  the  gas  and  are  reproduced  as  soon  as  removed.  They  require 
the  highest  degrees  of  supersaturation  for  condensation  and  are  without 
electrification. 

All  these  groups  may  be  made  to  pass  continuously  into  each  other. 

I  shall  use  the  term  "nucleation"  to  denote  the  number  of  nuclei  per 
cubic  centimeter  observed  in  any  experiment.  It  will  be  understood 
that  this  means  the  efficient  nucleation;  for  nuclei  may  be  and  usually 
are  present,  which  are  not  detected  by  the  exhaustion.  They  are  com- 
puted in  the  present  chapter  from  the  angular  diameter  (<f>**s/$o,  nearly) 
of  the  coronas,  for  a  given  supersaturation.  To  specify  their  number  one 
must  come  to  a  conclusion  as  to  whether  nuclei  are  removed  more  rapidly 
by  the  exhaustion  than  they  can  be  replaced  by  the  molecular  system, 
or  whether  the  reverse  is  the  case.  If  fleeting  nuclei  and  colloidal  nuclei 
are  supposed  to  be  instantly  reproduced  we  shall  call  the  number  n. 
None  are  then  virtually  removable  by  the  sudden  exhaustion.  Otherwise 
the  nucleation  (corrected  for  the  volume  expansion)  is  called  N.  In  this 
case  the  exhaustion  is  more  rapid  than  the  reproduction  of  nuclei.  Both 
n  and  N,  as  well  as  s,  will  usually  be  given  in  the  earlier  tables;  for  the 
discrimination  between  n  and  N  is  not  possible,  and  s  is  specially  favor- 
able to  the  small  nucleation  which  are  apt  to  be  crowded  out  of  the 
diagrams  for  n  and  N. 

Returning  to  the  subject  of  this  section,  I  may  state  that  the  radium 
used  was  a  weak  sample  (10  mg.,  10,000 X)  hermetically  sealed  in  a  thin 
aluminum  tube.  In  an  earlier  paper  I  showed  that  whereas  the  nuclea- 
tion produced  decreased  very  rapidly  with  the  distance  of  the  energizer 
from  the  outside  of  the  cylindrical  glass  fog  chamber,  the  number  of 
nuclei  within  was  apparently  the  same  throughout  the  length  of  the  axis. 
Pressure  differences,  however,  were  usually  kept  below  the  fog  limit  of 


DISTRIBUTION    WITHIN    FOG    CHAMBER.  3 

air.  As  the  aluminum  tube  was  carefully  sealed  (ground  screw  plug  and 
wax)  the  beta-  and  gamma-rays  are  here  alone  in  question,  and  as  the 
bottom  of  the  fog  chamber  through  which  the  radiation  passes  may  be 
1  cm.  thick  and  the  walls  are  everywhere  more  than  0.2  cm.  thick,  only 
the  more  penetrating  beta-rays  are  active  to  reenforce  the  gamma-rays. 
In  fact  the  earlier  work  showed  that  the  rays  after  passing  1  cm.  of  lead 
produced  an  amount  of  nucleation  only  30  per  cent  less  than  in  the 
absence  of  the  dense  barrier.  Thus  the  whole  phenomenon  is  practically 
a  question  of  the  intensity  of  the  gamma-rays. 

In  the  course  of  the  work,  curiously  enough  a  number  of  contradictory 
conclusions  were  reached,  and  it  will  therefore  be  advisable  to  report  the 
results  chronologically,  beginning  with  the  data  for  low  pressure  differ- 
ences. 


Table  i. — Distribution  of  nucleation  within  the  glass  fog  chamber  (43  cm.  long,  14 
cm.  in  diameter);  nucleator,  radium  in  thin  aluminum  tube,  dp  =  21  cm.  Radium 
at  Dcm.  from  end,  axially  without.  Lines  of  sight  (two  goniometers,  j,  and  s2)  15 
cm.  and  35  cm.  from  end  nearest  radium,  or  20  cm.  apart. 


D 

*i 

U 

A/,  X  10-3 

io-3xA/2 

Mean  {  $ 

Per 
cent. 

0  cm. 

20  cm. 

40  cm. 

co  (air) 

3-5 
3-2 
3-4 
3-4 
3-5 
2-5 
2.4 
2.6 
1.8 

2-3 

2-3 
.0 

3-3 
3-o 

3-4 
3-6 

3-3 
2-5 
2-5 
2.8 
2.0 
2-3 
2-3 
.0 

19 

17 
17 
19 
7 
6 
8 
3 
5 
4 
0 

16 
n 

17 
21 

16 
7 
7 
9 
3 
5 
4 
0 

17,200 
l6,200 

7,000 
8,000 

4,000 
4,000 

100 

45 
24 

2.  Data. — The  cylindrical  glass  fog  chamber  (fig.  1),  rigorously  free 
from  leakage,  was  placed,  with  its  axis  horizontal,  in  such  a  way  that  a 
prolongation  of  the  latter  intersected  the  radium  tube  at  a  distance,  D. 
Two  goniometers  with  their  lines  of  sight  about  20  cm.  apart,  and  15  and 
35  cm.  from  the  end  (bottom)  of  the  fog  chamber  nearest  the  radium 
tube,  were  used  nearly  at  the  same  time  for  the  measurement  of  the 
apertures  of  the  coronas  seen  along  the  axis.  Both  were  placed  with  the 
pins  nearly  contiguous  to  the  walls  of  the  cylinder,  so  that  the  eye  was 
at  a  minimum  distance  of  30  cm.  off.  All  the  phenomena  may  in  this 
case  be  more  clearly  observed  and  the  small  coronas  are  less  liable  to  drop 
out  before  the  measurement  has  been  completed.      The  source  of  light 


4  VAPOR    NUCLEI    AND    IONS. 

(Welsbach  mantle)  was  250  cm.  beyond  the  fog  chamber.  Usually  the 
angular  diameter  of  the  coronas  is  about  5/30.  In  table  1,  st  refers  to 
the  goniometer  nearer  the  radium,  s2  to  the  other,  and  A^  and  N2  are  the 
corresponding  nucleations,  when  D  is  the  distance  of  the  radium  tube 
from  the  end  of  the  cylinder. 

After  the  influx  of  filtered  air,  time  was  always  allowed  for  the  dissi- 
pation of  convection  currents.  There  was  some  difficulty  in  reading  both 
goniometers  consecutively  without  loss  of  time,  as  the  small  coronas  soon 
vanish  with  the  subsidence  of  the  fog  particles.  It  was  necessary  to 
cleanse  the  walls  carefully  before  beginning  the  work  to  obviate  deposits 
of  dew. 


Fig.  i. 


FIG, 


L 


-20  -10 

Fig.  2. 


Fig.  3. 


,2 

1 

c 

1 

*4 

c 

£ 

,1 

c 

c 

1 

Fig.  4. 


Figs,  i,  3,  4. — Types   of    cylindrical  fog  chamber.     Axial  section.     E,  exhaust  pipe; 

c,  cloth  partitions. 
FiG-  2.— Nucleation  (N)  due  to  weak  radium  at  different  distances  from  and  on  top 

(side  of  cylinder)  of  the  fog  chamber.     Table  1 . 


The  table  gives  evidence  of  a  small  difference  between  Nl  and  N3,  but 
this  is  here  unquestionably  an  observational  error,  particularly  as  its 
sign  is  often  reversed.  The  chart  (fig.  2)  then  shows  the  mean  number 
of  nuclei  within,  when  the  radium  is  at  £>  =  o,  20,  and  40  cm.  from  the 
end;   and  while  the  nucleation  drops  off  rapidly  from  100  to  45  and  24 


DISTRIBUTION    WITHIN    FOG    CHAMBER.  5 

per  cent,  respectively,  the  nucleation  within  is  about  constant  through- 
out the  45  cm.  of  length  of  cylinder.  At  least  an  internal  drop  to  less  than 
one-fourth  is  out  of  the  question,  as  the  diagram  shows.  It  must  be 
remembered  that  the  nucleation  is  produced  instantly  to  saturation,  that 
all  nucleation  will  vanish  with  the  removal  of  the  radium  to  infinity 
within  a  few  seconds,  and  that  the  ions  here  in  question  are  relatively 
large  nuclei  as  compared  with  the  colloidal  nuclei  of  dust-free  air.  The 
latter,  moreover,  are  quite  ineffective  at  the  observed  pressure  differ- 
ence, dp  =  21,  used.  If  larger  pressure  differences  appear  the  results  are 
usually  quite  different. 

3.  Explanation. — To  account  for  these  remarkable  results  is  difficult. 
Convection  is  probably  out  of  the  question,  though  it  will  be  quite  elim- 
inated in  the  following  experiments.  One  may  hazard  the  suggestion 
that  the  effective  agency  outside  of  the  cylinder  are  the  gamma-rays 
directly,  whereas  within  the  cylinder  the  ionization  produced  by  those 
rays  secondarily  is  in  question.  In  other  words,  the  gamma-rays  do  not 
act  here  directly,  but  the  nuclei  are  produced  by  corpuscles  set  free  by 
these  rays.  The  medium  within  the  cylinder  is  thus  in  a  state  resembling 
an  electrolytic  medium  having  the  same  ionic  pressure  throughout. 
It  is  this  ionic  pressure  depending  on  the  density  and  speed  of  the  cor- 
puscles which  is  transmitted  instantaneously  from  end  to  end  of  the 
cylinder.  To  refer  to  the  phenomenon  as  diffusion  would  be  obscure 
without  a  statement  as  to  what  diffuses.  The  ionic  nucleus  is  relatively 
a  fixture  and  could  not  diffuse,  in  the  time  specified,  to  the  far  end  of 
the  cylinder,  quite  apart  from  decay. 

4.  Further  experiments  with    radium.      High   exhaustions. — In   the 

preceding  experiments  the  wet  cloth  partition  was  about  10  cm.  above 
the  surface  of  the  water  below.  In  the  new  chamber  shown  in  fig.  3,  the 
distance  has  been  reduced  to  5  cm.  Under  these  circumstances  a  very 
marked  gradation  of  the  number  of  efficient  nuclei  was  observed  for  the 
first  time.  This  is  not,  however,  due  to  the  supposed  elimination  of 
convection,  but  rather  to  the  large  pressure  difference  applied  in  the 
experiments.  The  result  follows  in  table  2.  When  the  radium  tube  is 
placed  at  T  (fig.  1)  symmetrically  on  the  side,  the  metal  cap  virtually 
becomes  the  source  of  nuclei,  or  better,  it  seems  to  become  secondarily 
active  more  intensely  than  the  remainder  of  the  glass  chamber.  The 
coronas  obtained  with  two  goniometers  at  distances  11  and  36  cm.  from 
the  brass  end  and  35  and  10  cm.  from  the  glass  end  are  rapidly  larger  as 
the  brass  end  is  approached.  The  ratios  of  the  n- values  is  greater  than 
2:5.    These  conditions  are  retained  indefinitely  so  long  as  the  radium  is 


6  VAPOR    NUCLEI    AND    IONS. 

present,  showing  that  the  result  is  not  incidental.  As  both  ends  of  the 
chamber  were  about  equidistant  from  the  radium,  it  would  appear  to  be 
the  excess  of  the  secondary  radiation  from  the  metal  cap  which  is  in 
question. 

Table  2. — Distribution  of  nucleation  within  the  glass  fog  chamber  (as  in  table  1) 

and  allied  results. 


N  xio-3. 


N  Xio-3. 


I.  Radium  tube  on  side  of  glass  fog 
chamber.  Two  goniometers,  I  at 
11  cm.  and  II  at  36  cm.  from 
brass  cap,  46  cm.  from  glass  end. 
dp  m  26.0  cm. 


'{ 


No.  I 
No.  II 

No.  I 
No.  II 


6.6 

95 

4-7 

38 

6.6 

95 

4.4 

30 

[47 

59 

'47 
46 


II.  Radium  on  glass  end,  1  cm.  thick; 
observation  I  at  10  cm.  and  II 
at  35  cm.  from  end.     dp  =  26. 


No.  I  . 
No.  II. 


60 
47 


76 
38 


59 


A/Xio-3.   AT  xio-8. 


III.  Radium  at  00  .     Lapse  10  m. 

26.5 
30.8 

27-4 

11 
114 

17.4 
195 

IV.  Radium  on  brass  plate,  1  cm. 
thick. 

30.6 

4.0 

24 

42 

1  Three  hours  later  no  interference. 


2wrg. 


5.  The  same,  continued.  X=rays. — After  finding  that  the  fleeting 
nucleation  within  the  fog  chamber  was  unequally  distributed  under  the 
excitation  of  radium,  similar  experiments  were  tried  with  the  X-rays, 
using  the  fog  chamber  (fig.  4)  with  four  horizontal  wet  cloth  partitions 
2  to  3  cm.  apart  to  obviate  convection.  The  results  given  in  the  first 
part  of  the  following  table  are  definitely  affirmative.  When  the  X-ray 
bulb  is  near  the  fog  chamber,  the  nucleation  nearer  the  bulb  is  decidedly 
in  excess.  Thus  when  the  line  of  sight  is  30  and  50  cm.  from  the  anti- 
cathode,  the  farther  nucleation  is  about  60  per  cent  of  the  nearer. 

If,  however,  the  bulb  is  relatively  far  away  (D  =  ioo  or  200  cm.),  the 
end  of  the  fog  chamber  farthest  from  the  bulb  and  near  the  brass  cap  is 
more  actively  ionized.  In  other  words,  under  these  circumstances  the 
secondary  radiation  from  the  brass  cap  predominates.  The  nucleation 
at  10  and  30  cm.  from  the  latter  shows  a  decrement  of  20  per  cent,  for 


DISTRIBUTION    WITHIN    FOG    CHAMBER.  7 

instance,  passing  continuously  from  the  high  to  the  lower  values.  This 
experiment  throws  light  on  the  function  of  the  walls  in  producing  dis- 
tributions in  case  of  persistent  nuclei.  Obviously  the  effect  of  secondary 
radiation  decreases  rapidly  as  the  distance  from  the  walls  increases.  The 
nucleation  within  the  fog  chamber  is  probably  largely  due  to  this  kind 
of  radiation. 

6.  The  same,  continued.  Miscellaneous  tests. — In  the  second  part 
of  table  3,  experiments  with  radium  are  resumed  for  comparison.  The 
gradation  of  number,  decreasing  from  the  brass  end  to  the  glass  end,  for 
a  symmetrical  position  of  the  radium  tube  at  T,  fig.  i,  is  very  marked, 
as  usual;  while  the  case  for  radium  at  R,  fig.  i,  again  shows  the  largest 
coronas  at  the  end  of  the  tube,  the  distribution  being  more  nearly  uni- 

TablE  3. — Distribution  of  ions  within  glass  fog  chamber.  Metallic  (brass)  cap  at  one 
end,  glass  end  opposite  1  cm.  thick.  Lines  of  sight  10  cm.  (s10)  and  30  cm.  (sx) 
from  brass  end,  15  cm.  and  35  cm.  from  glass  end.     X-rays  acting  from  distance  D. 


Lead  case. 

D. 

"^10- 

**>■ 

Ni0  X  10-3. 

N„  X  10-3. 

dp. 

cm. 

I  off 

15 
15 

GBP 

WPcor 

130 
180 

156 

255 

24-5 
30 

w  P  cor 

wrg 

15 

w  P  cor 

wog 

180 

300 

30 

1 

w  P  cor 

wog 

180 

300 

30 

hoo 

6.9 
w  0 

6.3 

wg 

121 

9i 

30 

II  off: 

^00 

6-5 

6.1 

102 

84 

30 

On  middle  of  side  at  T. 

•••{ 

6.8 
6.6 

5-4 
5-o 

114 
106 

63 
48 

30 
30 

On  glass  end  at  R. .  . 
On  side  near  cap  at  S. 
On  middle  of  side  at  T. 
On  side  near  glass  end 

5-6 
4-4 
6.4 

5-2 

3-3 
4-5 

69 
33 
96 

56 
H 
36 

30 
30 
30 

at  S1 

4.8 

4.8 

45 

45 

30 

Large  coronas  near  brass  cap.     Secondary  radiation  preponderating. 


form.  Thereafter  the  radium  was  placed  in  positions  5,  T,  S\  on  top, 
successively,  with  the  results  for  T  graded  about  as  usual.  Radium  at 
5  still  evokes  gradation,  but  the  coronas  are  even  much  smaller  than 
when  the  radium  is  placed  on  the  thick  glass  end  at  R.  When  radium  is 
placed  at  S'  near  the  glass  end  gradation  is  nearly  absent,  but  the  coronas 
are  again  small.  The  results  are  therefore  not  as  simple  as  was  antici- 
pated and  do  not  admit  of  an  explanation  merely  in  terms  of  the  glass 
penetrated. 


8 


VAPOR    NUCLEI    AND    IONS. 


When  the  radium  tube  is  attached  to  the  glass  end  (about  i  cm. 
thick),  similar  gradations  are  observed,  but  this  time  with  the  large 
coronas  near  the  radium  tube.  (See  fig.  5.)  The  ratio  of  n- values  is 
now  about  2  for  the  given  distances.  The  law  of  variation  is  difficult  to 
obtain  in  any  of  these  cases,  but  when  the  brass  end  is  predominatingly 
active,  the  reduction  of  n- values  is  nearly  proportional  to  distance,  if 
the  usual  mean  values  of  5  be  taken  together  with  the  special  observa- 
tions. 


120 


80 


60 


20 


\ 


m 


Rad. 

brass 

end 


DISTRIBUTION  WITHIN  FOG 


VA 


V*. 


***j* 


V 
Radid/n  on  $i)sfe  6p 


>D 


&N 


FIG 


26 


CHAMBER 


w 


/ 


/- 


**£ 


<**•" 


J* 


^^•O- 


Radiurr  ong/as.  I  end,  op  =26    <•  ^  o 


^ 


A0$ 


I  CI 


20 


Fig.  5. — Density  of  ionization  (A7)  within  the  fog  chamber  at  different 
distances  (D)  from  the  brass  end.     Table  2. 


In  view  of  the  action  of  the  glass  end  when  the  radium  is  attached 
to  it,  it  seems  possible  that  the  glass,  large  thicknesses  of  which  are 
always  penetrated  and  permeated  obliquely  by  the  radiation,  may  be 
active  in  both  cases,  but  special  inquiry  is  needed  here.  The  glass 
cylinder  was  found  to  be  thinner  (about  0.15  cm.)  near  its  equatorial 
parts  (7),  and  to  increase  in  thickness  towards  both  ends.  If,  how- 
ever, the  phenomena  were  due  to  thickness  of  glass  the  coronas  should 
be  largest  near  the  middle  and  taper  down  toward  both  ends  of  the  fog 
chamber.  This  is  not  the  case,  as  the  coronas  for  a  symmetrical  position 
of  the  radium  tube  decrease  regularly  from  the  brass  to  the  glass  end 
of  the  apparatus. 

If  the  radium  tube  is  placed  on  the  outside  of  the  brass  cap,  one 
cm.  thick  or  more,  there  is  the  usual  moderate  reduction  of  nucleation 
here,  from  n  =  6$  to  ^  =  24  thousands  (63  per  cent);  but  the  change  of 
diameter  of  coronas  within  is  of  the  same  kind,  decreasing  from  the 
brass  to  the  glass  end,  as  above. 


DISTANCE    EFFECT.  9 

7.  Distance  effects  of  radium. — To  throw  further  light  on  present  and 
preceding  questions  at  issue,  I  shall  next  anticipate  some  of  the  work 
below  and  describe  certain  experiments  specially  adapted  for  the  pur- 
pose. By  "dust-free  air"  I  mean  atmospheric  air  filtered  with  extreme 
slowness  (through  large  wide  filters  of  packed  cotton)  and  thereafter 
left  without  interference  for  two  or  more  hours.  Such  air  shows  a  high 
fog  limit.  In  the  fog  chamber  used  the  condensation  began  at  an 
observed  pressure  difference  of  about  dp  =  26  cm.;  rain-like  condensation 
at  dp  =  21  cm. 

In  the  present  experiments  all  tests  are  made  at  dp  =  41.$  cm.,  at 
a  pressure  difference  therefore  much  above  the  fog  limit,  and  probably 
approaching  the  condensing  power  of  the  apparatus.  The  number  of 
nuclei  computed  from  the  coronas  observed  is  an  estimate  merely,  as 
the  constants  needed  for  the  very  large  range  of  variation  in  question 
are  not  available.  Nevertheless  if  the  same  dp  is  used  throughout,  the 
nucleations  obtained  are  immediately  comparable.  With  these  reser- 
vations the  number  of  nuclei  found  in  the  dust-free  air  and  at  the  dp 
in  question  is  about  N  =  380  X  io3  to  400  X  io3,  per  cubic  centi- 
meter. It  is  obvious,  moreover,  that  these  nuclei  are  excessively  small, 
much  smaller  than  ions,  smaller  even  than  those  which  would  respond 
to  smaller  dp's  exceeding  dp  =  26  cm. 

Let  the  fog  chamber  (fig.  1)  be  subjected  to  the  radiations  from  weak 
radium  (10,000  X,  10  mg.)  contained  in  a  thin  hermetically  sealed 
aluminum  tube.  As  the  walls  of  the  fog  chamber  are  0.1  to  0.3  cm.  thick 
and  the  end  (bottom)  toward  the  tube  nearly  1  cm.  thick,  y-rays  only 
will  penetrate  into  the  inside,  apart  from  the  secondary  radiation  there 
produced.  As  shown  in  fig.  1  (cylindrical  fog  chamber)  the  radium 
tube  R  is  at  an  axial  distance  D  from  the  nearer  end.  In  addition  to 
this  the  radium  was  also  tested  at  T  (top)  in  the  figure,  where  it  is 
nearest  the  body  of  dust-free  air  under  experiment. 

The  data  investigated  are  shown  in  table  5  and  in  the  curve  (fig.  6), 
where  the  abscissas  are  the  distances  D  and  the  ordinates  the  number 
of  efficient  nuclei  per  cubic  centimeter. 

It  follows  from  the  graph  that  as  the  radium  is  brought  in  an  axial 
direction  from  00  to  the  end  of  the  fog  chamber,  the  number  of  efficient 
nuclei  in  the  dust-free  air  contained  is  gradually  but  enormously  reduced 
to  a  minimum  for  D  =  2$  cm.  (about),  after  which  the  number  again 
increases  to  the  maximum  at  D  =  0.  Curiously  enough,  when  the  radium 
was  further  approached  to  the  body  of  the  air  by  being  placed  at  T, 
the  mean  number  of  nuclei  did  not  increase.* 

*This  result  is  to  be  further  interpreted  in  special  experiments  below. 


IO 


VAPOR    NUCLEI    AND    IONS. 


If  the  radium  is  inclosed  in  a  long,  thick  lead  tube  (60  cm.  long,  walls 
0.5  cm.  thick),  the  nucleation  is  but  moderately  reduced  (see  crosses  in 
fig.  6),  showing  that  gamma-rays  are  in  question. 

Table  4. — Radium  effect  at  high  pressure  differences,     dp  =41.5  cm.;   s  (air)  =7.5;  D, 
distance  from  end  of  fog  chamber. 


D. 

s. 

n  X10-3. 

D. 

s. 

n  x  10-3. 

On  top. . 

3-9 

27 

50 

4-8 

51 

3 

9 

27 

4 

•9 

54 

25 

3 

3 

16 

100 

6 

3 

104 

3 

4 

17 

6 

8 

129 

0 

4 

8 

51 

00 

7 

,1 

160 

4 

7 

48 

End 

4 

8 

51 

On  top. . 

4 

0 

27 

4 

7 

48 

4 

1 

31 

Top 

4 

6 

44 

0 

4 

4 

37 

4 

7 

48 

4 

7 

48 

End 

4 

7 

48 

25 

3 

3 

16 

Top 

4 

7 

48 

>o 

4 

1 

3i 

2End 

4 

7 

48 

On  top . . 

4 

0 

27 

00 

6 

97 

xOn  top.. 

3-9 

27 

1  Radium  tube  in  lead  pipe  walls  5  cm.  thick.  *  Lead  radiation. 


0& 

ftp** 

FIG. 

6 

J, 

'AN) 

(JO 

-3 

y\ 

h 

V 

-cfc^^ij 

%*JQ~* 

fp-22 

*»D 

40 


60 


do 


100 


120 


Fig.  6.— Efficient  nucleation  (JV)  near  the  middle  of  the  fog  chamber,  for  different  dis- 
tances (D)  of  radium  from  the  end  and  for  different  exhaustions  (dp).  Table  4. 

8.  Cause  of  the  minimum  and  the  maximum.— This  is  easily  explained, 
since  the  ions  are  relatively  large  bodies  and  relatively  few  in  number 
as  compared  with  the  nuclei  of  dust-free  air  for  the  same  dp.  Hence 
the  ions  capture  the  moisture  more  and  more  fully  as  their  number, 
with  diminishing  distance  D,  becomes  greater.  At  #  =  25  cm.  probably 
the  whole  of  the  moisture  is  condensed  on  ions,  and  as  their  number 
increases  as  D  vanishes  the  minimum  in  question  results.     In  fact,  it 


DISTANCE    EFFECT. 


II 


was  shown  elsewhere  that  below  the  fog  limit  of  air,  the  nucleation 
observed  and  due  purely  to  radium  at  different  distances,  D,  is,  for 
example  (dp  =  2 2), 


D 

N  x  io~8 


o 

20 


10 

50 


30 

32 


50         100 

20  12  etc., 


agreeing  in  character  as  far  as  may  be  expected  with  the  data  here  in 
question.  These  data  multiplied  by  4  (in  other  words  4n  X  io~s) 
are  also  given  in  fig.  6  for  comparison.  Hence  the  ions  caught  at  dp  = 
41.5  are  about  four  times  more  numerous  than  at  dp  =  22,  and  corre- 
spondingly smaller.  They  behave,  therefore,  as  if  they  were  markedly 
graded,  but  nevertheless,  as  a  group,  throughout  much  smaller  than 
the  nuclei  of  dust-free  air  so  long  as  the  radiant  field  is  appreciable. 
While  the  number  of  nuclei  continually  grows  smaller,  with  dimin- 
ishing D,  the  efficient  nuclei  may  nevertheless  increase  again  below  a 
certain  D,  seeing  that  the  colloidal  nuclei  in  dust-free  air  are  enor- 
mously in  excess,  only  a  few  of  which  are  caught  even  in  the  absence  of 
radium. 

Table  5. — Distance  effect  of  radium.     D  measured  from  side.     Sp~  35  cm. 


D. 

s. 

n  x  io~s. 

n  xio-3. 

cm. 

250 

200 

150 

100 

50 

25 

12 

0 

cm. 
»7.6 
'7-6 
>7.6 
s73 
45-i 
4.4 
4.2 
4-7 

160 

150 

145 

136 

56 

35 

30 

45 

300 

285 

270 

255 

105 

66 

57 

84 

Radium  at  00.     Lapses  15s  and  3m. 

00 
00 

4.1 
l7-6 

27 
160 

5i 
300 

'GBP. 


2gyog'.        »wog. 


4wrg. 


It  would  be  more  difficult  to  account  for  the  result  that  the  same 
nucleation  is  observed  wherever  the  radium  touches  the  outside  of  the 
elongated  fog  chamber.  In  otherwords,  radium  at  the  end  of  the  chamber 
in  the  earlier  experiments  seemed  to  produce  the  same  mean  nucleation 
as  when  at  the  top,  although  the  distances  from  the  center  of  mass  of 
the  glass  are  as  3  to  1 ;  but  the  above  experiments  have  already  sug- 
gested that  this  result  was  probably  an  incidental  case. 


12 


VAPOR    NUCLEI    AND    IONS. 


320 


240 


9.  Further  experiments  with  radium. — Incidental  experiments  corre- 
sponding to  those  of  the  preceding  section  are  given  in  table  6,  showing 
the  reduction  of  the  efficient  nucleation  of  dust-free  air  when  the  radium 
tube  is  gradually  approached  to  the  sides  of  the  chamber.  They  are 
shown  graphically  in  fig.  7,  both  in  relation  to  s,  ft,  and  N,  and  need 
little  discussion.  The  minimum  position  lies  very  near  the  chamber 
and  about  10  cm.  from  it.    The  action  of  radium  is  hardly  perceptible 

beyond  1  meter,  chiefly 
because  the  green-blue- 
purple  corona  happens  to 
be  involved.  Sharper  re- 
sults could  therefore  be 
obtained  at  lower  pressure 
differences,  where  white- 
red-green  coronas  are  in 
question.  But  on  the 
whole  it  is  clear  that  ra- 
diation which  appreciably 
lowers  the  asymptote  cor- 
responding to  dust-free 
non-energized  air  must  be 
of  an  intensity  exceeding 
the  effect  of  10  mg.  of  weak 
radium  (10,000  X),  at  a 
distance  of  1  meter.  There 
not,  therefore,  seem 
to  be  much  hope  of  ob- 
serving cosmical  radiations 
in  this  way.  Finally  the 
second  part  of  table  6  (and 
other  data  below)  shows 
how  soon  the  high  nuclea- 
tions  of  dust-free  air  (non-energized)  is  regained  after  the  removal  of 
the  radium  tube.  The  rapidity  with  which  ionized  nuclei  fall  apart  is 
obtainable  in  this  way  and  well  worthy  of  special  research.  (Cf.  Section 
62  et  seq.) 


40 

uxp-3  does 


Fig.  7. — Efficient  nucleation  (N)  and  coronal  aper- 
ture (S)  for  different  distances  (D)  of  radium  from 
end  of  fog  chamber  and  for  different  exhaustions 
(dp).    Table  5. 


10.  Distance  effect  of  penetrating  X-radiation.— The  question  at  issue 
was  whether  the  rays  which  have  penetrated  lead  are  characterized 
by  the  same  marked  distance  effect  which  is  observed  for  radium.  The 
fog  chamber  was  inclosed  in  a  close-fitting  lead  casket  with  two  narrow 
side-windows  for  observation.    The  end  of  the  casket  toward  the  bulb 


DISTANCE    EFFECT. 


13 


was  provided  with  a  lid  to  be  opened  or  closed  at  pleasure.  When  the 
distance  is  D  =  $o,  about  8  per  cent  of  the  radiation  passes  through; 
when  D  =  io  cm.  the  amount  is  about  17  per  cent.  Unfortunately  the 
observation  through  the  window  is  not  satisfactory  and  no  doubt  a 
certain  amount  of  radiation  enters  here  secondarily.  It  is  therefore 
difficult  to  carry  out  the  comparison. 

Tabids  6. — Penetration  through  lead.    Lead-cased  glass  fog  chamber.    Plates  of  lead 
0.14  cm.  thick.    dp=  24.5. 


Lead  case — 

D. 

s. 

n  X  io-s. 

On ;  end  closed 

50 

50 
10 
10 
10 
15 

15 

2.7 

3-1 
gBP. 

3-8 

3-5 

3-5 
wog  7.0 
j  gBP  to 
\  w  P  cor. 

6.7 
9-5 
too 
19-5 
16.5 
16.5 
104 
130 
156 

On;  end  open 

On ;  end  closed 

On ;  end  closed 

On ;  end  closed 

Off ;  plate  only 

Off ;  no  plate 

Large  coronas  near  brass  cap.     Secondary  radiation. 

11.  General  inferences. — The  occurrence  of  a  continuous  succession 
of  groups  or  gradations  of  nuclei  in  the  curve  of  figs.  6  and  7,  each  of 
which  groups  constitutes  a  condition  of  chemical  equilibrium  for  the 
given  radiating  environment,  is  suggestive.  In  the  first  place,  it  may  be 
recalled  that  the  nuclei  of  dust-free  air  are  an  essential  part  of  this  body 
as  much  as  the  molecules  themselves.  Such  nuclei,  if  withdrawn  by 
precipitation,  are  at  once  restored.  Again,  air  left  without  interference 
for  days  shows  a  maximum  of  this  nucleation  for  the  given  conditions  of 
exhaustion  when  all  foreign  nucleation  must  have  vanished.  Indeed, 
the  water  molecules  themselves  may  be  treated  as  a  continuous  part 
of  the  nucleation  in  question,  the  frequency  of  occurrence  being  a  maxi- 
mum for  the  molecular  dimensions.  It  is  best,  however,  to  reserve  dis- 
cussion for  a  later  paragraph  (section  43). 

THE   NUCLEATION   OF  FILTERED  AIR  IN   RELATION  TO  DIFFERENT 
SUPERSATURATIONS  OF  WATER  VAPOR. 


12.  Successive  series  of  results. — Before  proceeding  with  an  account 
of  the  change  of  the  efficient  colloidal  nucleation  of  atmospheric  air  in 
the  lapse  of  time  and  other  like  problems,  it  is  expedient  to  consider  the 
behavior  of  filtered  air  when  subjected  to  different  exhaustions.     I  will 


I4  VAPOR    NUCLEI    AND    IONS. 

proceed  chronologically,  taking  the  earliest  experiments  first.  These 
may  be  given  with  sufficient  detail  in  a  chart  like  figure  8,  in  which 
the  lower  graph  (I)  shows  the  data  obtained  in  the  earlier  memoirs 
with  a  wooden  fog  chamber.  The  observed  pressure  differences  (super- 
saturations)  are  laid  off  horizontally,  the  apertures  of  the  coronas 
(5  =  ^/30,  nearly,  where  <j>  is  the  angular  radius  to  the  outside  of  the  first 
ring,  when  the  eye  and  the  source  of  light  are  at  distances  85  and  250 
cm.  on  opposite  sides  of  the  fog  chamber)  and  the  nucleations  vertically. 
No  particular  attention  was  given  to  the  occurrence  of  rain,  and  the 
measurements  cease  at  the  lower  end  with  the  measurably  visible 
coronas.  It  is  seen  that  the  curve  very  soon  reaches  an  asymptote, 
showing  hopelessly  poor  efficiency.  As  the  work  was  carefully  done, 
the  only  explanation  would  seem  to  be  that  the  speed  of  filtration  was 
insufficiently  slow  and  the  exhaustion  insufficiently  rapid  (small  vacuum 
chamber).  The  same  remarks  apply  to  the  graph  (figure  8,  II),  ob- 
tained in  a  decreasing  march  of  pressure  difference,  at  the  beginning 
of  the  work  with  the  glass  fog  chamber  (fig.  1);  but  the  asymptote  is 
higher.  The  fog  limit  in  this  case  is  lower  and  attributable  to  nuclei 
which  have  entered  unobserved,  as  it  is  much  below  the  values  for 
more  carefully  filtered  air.  The  first  observation,  having  been  made 
with  the  apparatus  at  rest  for  12  or  more  hours,  shows  a  very  high  but 
probably  more  nearly  correct  result. 

Figure  8  also  contains  the  corresponding  nucleations,  N,  so  far  as 
they  can  be  computed,  supposing  that  the  nuclei  are  removed  faster 
than  they  can  be  restored.  For  high  pressure  differences  the  data  are 
necessarily  estimates.  Naturally  the  differences  between  the  data 
obtained  after  long  waiting  (12  hours  or  more),  and  those  obtained  in 
succession  after  intervening  intervals  of  a  few  minutes,  are  enormously 
accentuated. 

It  follows  from  these  results  that  if  normal  data  were  to  be  reached 
it  would  in  the  first  place  be  necessary  to  perfect  the  method  of  filtration. 
This  was  done  by  providing  the  filter  with  a  very  fine  screw  stopcock, 
by  which  the  rate  of  flow  through  the  filter  could  be  diminished  very 
gradually  to  a  vanishing  value. 

The  next  group  of  results,  obtained  on  May  21,  23,  and  30,  and  on 
June  3,  were  found  under  conditions  of  very  slow  filtration.  They  are 
sufficiently  reproduced  in  the  graphs  (figs.  9, 10, 1 1)  ,in  which  the  abscissas 
are  the  pressure  differences  and  the  ordinates  the  coronal  diameters  (s) 
and  the  nucleations  (n  and  N)t  respectively,  as  specified.  The  graphs  for 
5  are  perhaps  most  suitable  for  discussion,  although  s  exhibits  the  small 
nucleations  with  very  great  advantage.  The  data  for  May  21  are  in 
the  main  much  above  those  in  fig.  8,  but  they  are  still  far  too  low  and 


EFFICIENCY    OF    FOG    CHAMBER. 


15 


irregular.  The  other  data  are  much  larger  and  as  far  as  dp  =  30  lie 
sufficiently  near  together  to  show  that  limiting  conditions  are  being 
approached.  Beyond  this  the  curves  diverge  widely.  The  highest 
results  reached  are  those  of  May  30.  On  June  3  a  change  takes  place 
during  the  course  of  the  experiment,  as  the  result  of  which  the  incoming 
and  outgoing  curves  differ.  In  all  cases  there  is  a  distinct  tendency  to 
approach  a  limit  after  dp  exceeds  37  cm.,  due  to  the  limitations  of 
the  apparatus. 


Figs.  8,  9,  and  10. — Early  data  of  efficient  nucleations  (N,  n)  and  coronal  diameter  (j), 
appearing  at  different  exhaustions  (dp)  in  dust-free  air.     Imperfect  fog  chamber. 

The  characteristic  feature  of  all  the  nucleation  curves  is  the  rapid 
increase  between  dp  =  27  and  30  cm.;  that  is,  during  the  early  coronal 
stages.  Below  this  the  relatively  large  nuclei  are  present  at  least  as  far 
as  dp  =  21  to  the  extent  of  a  few  thousand  per  cubic  centimeter.  Never- 
theless, it  is  their  variation  which  brings  about  the  sinuous  outline  of 
the  curves  above  dp  =  33,  seeing  that  large  nuclei  are  overshadowingly 
effective. 


i6 


VAPOR    NUCLEI    AND    IONS. 


On  the  5th  and  6th  of  August  a  series  of  experiments  was  made  to  test 
the  effect  of  long  and  short  lapses  of  time  between  the  observations,  as 
well  as  the  displacements  of  lower  limits  of  the  curves.  The  results 
of  August  6  at  ^«=35  show  that  15  minutes  was  an  insufficient  time 
between  observations,  but  that  intervals  exceeding  30  minutes  (very 


600 


500 


NxlO'9 


Figs.  Il,  12,  13,  and  14. — Early  data  of  efficient  nucleations  (A/,  n)  and  coronal  diam- 
eter (s),  appearing  at  different  exhaustions  {dp)  in  dust-free  air.  Imperfect  fog 
chamber. 

slow  filtration  presupposed)  are  liable  to  show  the  true  efficient  nucle- 
ation  at  the  time  of  experiment.  Direct  experiments  made  under  con- 
ditions show  that  intervals  of  from  one  to  two  hours  will  in  all  cases 
be  sufficient  for  the  decay  of  extraneous  nuclei. 


EFFICIENCY    OF    FOG    CHAMBER. 


17 


Table  7. — Nucleation  of  dust-free,  non-energized  and  energized  air,  different  exhaus- 
tions, dp.  Lapse  about  15  min.  Barometer,  75.97  cm.  Piping  and  stopcock  of 
1 -inch  gas  pipe. 


dp. 

s. 

n  x  10-3. 

N  X  io-s. 

dp.         s. 

n  X  io-s. 

N  x  io-s. 

I.  1 

Dust-free  air  not  energized. 

IV  (continued).    X-ray  bulb.     D  =  100 
cm.;  fronting  bottom.4 

35.1 

26.0 

6.2 
2 

94 
27 

180 
3-9 

22.7 

5-6 

59 

85 

26.3 
24.2 

2-3 

1.2 

3-8 
1.4 

5-8 
2.1 

20.9 

18.8 

4-9 
•?.9 

?I.O 

1 . 2 

37 
•9 

53 
?i.i 

?1.2 

1.6 

22.6 
22.6 
21  .O 

(?) 

1:2 

(?) 
.2 
.0 

(?) 
•3 
.0 

19.0 
19.0 

•9 
1 . 2 

V.  X-ray  bulb.     D  =  50  cm. 

II.  Ra< 

iium   on   middle  of  s 
chamber. 

ide  of  fog 

19.0 

1 .2 

1 .2 

1-7 

VI.  X-ray  bulb.   D  =  25  cm. 

21.0 
19.0 
19.0 

3-3 
(?) 
1.5 

11 

(?) 
.2 

15 
(?) 
.3 

19.2 

« 

1.8 

2.4 

20. 1 

2. 1 

25 

3-4 

19.2 

1-3 

1.8 

22.4 
24.1 

4.8 
4-9 

37 
4i 

53 
61 

18.2 
18.2 

.0 
.0 

.0 
.0 

.0 
.0 

26.0 

5-2 

52 

80 

30.0 

5-2 

55 

93 

VII.  D=$o  cm.  above8  fog  chamber. 

35-0 

51 

56 

106 

1.6 

19.0 

1 

V 

1 . 2 

III.  Dust-free  air. 

19.9 

2 

9 

6.7 

91 

20.9 

4 

4 

26 

36 

35o 

6.2 

94 

180 

21.3 

5 

6 

54 

77 

33-0 

5-8 

80 

*43 

22.7 

5 

8 

63 

9i 

Sl.l 

5-5 

68 

117 

24.4 

wrg   7 

3 

117 

175 

29- 3 

5-2 

54 

9i 

26.  2 

wog^ 

8 

130 

200 

27.6 

31 

10 

16 

27.7 

wo/g7 

8 

135 

217 

28.1 

3-8 

21 

34 

29.8 

gBP8 

3 

150 

249 

26.3 

2.1 

3 

4-7 

933-0 

gBP 

156 

281 

28.1 

3-8 

21 

34 

34-9 

gBP 

160 

303 

29.6 

4-7 

4i 

70 

38.3 

gBP 

167 

346 

31 -2 

5-3 
5-8 

60 
80 

103 

42.0 

wog>  7 . 9 

?i74 

?4QO 

33- 1 

143 

35-2 

s5-8 

82 

155 

VIII.  D=6oo  cm.  from  end. 

IV.  X- 

ray  bulb.    D  =  100  cm 

.;  fronting 

35-0 

104-4 

35 

67 

bottom.4 

33-7 

4.6 
4.6 

4i 

75 
68 

31.0 

40 

42.0 

57-o 

146 

338 

28.0 

4.6 

37 

60 

41.4 

'7.0 

H5 

332 

25.8 

4.6 

36 

56 

35o 

67-o 

134 

255 

24.2 

4.6 

35 

52 

30.7 

57-2 

131 

222 

22.7 

4-3 

26 

38 

26.2 

6-5 

94 

146 

20.9 

3-o 

7-7 

11 

24.0 

6.2 

79 

"3 

19.7 

i-3 

i-3 

1.8 

1  Vanishing  at  once  and  faint,  only  just  visible. 

*  Nothing  (fog  or  rain)  observed. 

'  Accidental  slow  reopening :    same  result. 
♦Exposure  a  minutes.      No  increment  of  N 
results. 

*  All  large  wrg  coronas. 
•Coronas  clear  but  too  small. 


7  Bottom  of  glass  i  cm.  thick,  interferes  with  for- 
mation of  persistent  nuclei  even  at  short 
distances  like  25  cm.  =  i>. 

•Persistent  nuclei  just  begin  to  be  generated. 
a  <  0.5  cm.  maximum  for  fleeting  nuclei. 

9  Next  day. 

10  Smaller  than  air  coronas ;  a  always  taken. 


i8 


VAPOR    NUCLEI    AND    IONS. 


13.  Effect  of  X-rays  and  gamma=rays.  Data. — To  interpret  the  above 
results  it  will  be  necessary  to  vary  the  nucleations  of  the  dust-free  air 
artificially,  by  acting  on  it  from  the  outside  of  the  chamber  with  the 
X-rays,  or  with  the  gamma-rays  of  radium. 

In  these  experiments  the  glass  fog  chamber  (fig.  i),  rigorously  free 
from  leakage,  was  used  with  a  framework  of  wet  cloth  within.  Filtration 
was  throughout  excessively  slow  and  all  other  precautions  were  taken. 
The  radium  in  the  hermetically  sealed  aluminum  tube  was  pasted  to  the 
top  of  the  fog  chamber  at  T.  The  X-ray  bulb  was  adjustable,  so  as  to 
act  from  different  positions  at  distances  D. 

Table  8  shows  results  where  dp  is  the  pressure  difference,  5/30  the 
angular  coronal  diameter,  when  the  distances  of  the  eye  and  the  lamp 
are  35  cm.  and  300  cm.  from  the  fog  chamber.  The  small  distances  D 
(35  cm.)  enabled  the  observer  to  see  even  the  smallest  coronas  distinctly. 
The  nucleation  n  is  obtained  by  supposing  that  the  nuclei  are  restored 
faster  than  they  can  be  removed  by  exhaustion.  In  case  of  N  this  is  not 
the  case,  so  that  the  correction  for  volume  expansion  is  added.  For 
high  pressure  differences  the  absolute  numbers  are  not  trustworthy,  but 
the  data  given  nevertheless  show  the  relations  satisfactorily. 


Table  8. — Persistent  nuclei.     Exposure  2m.     D  measured  from  anticathode  to  top 
of  fog  chamber.     Thick  (1  mm.)  aluminum  screen  (earthed)  interposed. 


D. 

dp. 

s. 

N  x  io-8. 

Lp. 

D. 

dp. 

s. 

N  x  io~3. 

Lp. 

cm. 

cm. 

min. 

cm. 

cm. 

min. 

12 

18.0 

7.8 

140 

0 

30 

18.2 

3-o 

9 

1 

20 

18 

6 

5-3 

56 

0 

18.2 

3-2 

12 

0 

18 

4 

5-7 

67 

1 

50 

18.4 

.0 

0 

0 

30 

18 

0 

2 

0 

40 

18.3 

2.7 

7.2 

1 

18 

0 

*4-o 

22 

1 

18.0 

1 .0 

1 . 2 

1 

17 

5 

3.o 

9 

2 

18.0 

1 .0 

1.2 

1 

18 

2 

2.7 

7 

0 

50 

18.0 

*a 

.  1 

2 

18  2 

l3-i 

10 

1 

•5 

.  1 

1 

1  Spontaneous  generation. 


8  Just  visible  before  falling. 


The  data  of  table  8  are  constructed  in  the  charts,  figs.  1 5  to  1 7,  showing 
the  5,  w,  and  N  curves  in  succession,  for  increasing  supersaturations. 
They  will  be  useful  for  comparison  with  the  advanced  work  below. 


14.  Persistent  nuclei.— Table  8  gives  the  corresponding  data  for 
persistent  nuclei.  Distances  are  here  measured  from  the  sides  of  the 
fog  chamber  where  the  glass  was  thinner  (about  0.2  cm.)  than  at  the 
end  (1  cm.).     No  persistent  nuclei  were  obtained  when  the  radiation 


EFFICIENCY    OF    FOG    CHAMBER. 


19 


passed  through  the  end  of  the  fog  chamber  as  in  table  7.  To  guard 
against  direct  inductive  action  the  fog  chamber  was  covered  with  an 
earthed  plate  of  aluminum,  0.5  mm.  thick,  though  this  precaution  is 
superfluous.     The  table  shows  the  distance  (D)  of  the  anticathode  above 


&BP 


Figs.  15  and  16. — Early  data  of  efficient  nucleations  (N,  n)  and  coronal  diameter  (s), 
appearing  at  different  exhaustions  (dp)  in  dust-free  air.  Imperfect  fog  chamber. 
(Illustrating  table  7.) 

the  fog  chamber,  the  coronal  diameter  (5/30),  the  nucleation  (N;  n  would 
have  no  meaning  here) ,  and  the  time  elapsing  (Lp) ,  after  the  radiations 
are  cut  off  until  the  observations  are  made.  The  time  of  exposure  was 
uniformly  2  minutes.     Longer  exposures  would  have  produced  seriously 


20 


VAPOR    NUCLEI    AND    IONS. 


distorted  coronas.     These  data  are  constructed  in  fig.  18,  the  s  values 
being  dotted  and  the  TV  values  drawn  in  full. 


120 


300 


200 


Fig.  17. — Nucleation  (N)  for  different  exhaustions  (dp)  and  radiations. 

Bulb  distance. 
Fig.  18. — Persistent  nucleation  (N)  produced  by  X-rays  acting  from 

different  distances  (D)  from  the  glass  fog  chamber.     Table  9. 

15.  Persistent  nuclei  generated  through  tin  plate. — In  view  of  the 
ease  with  which  the  cylindrical  fog  chambers  may  be  made  rigorously 
air-tight,  it  seemed  worth  while  to  endeavor  to  produce  persistent 
nuclei  through  a  plate  of  tinned  sheet-iron,  0.03  cm.  thick  and  14  by 
20  inches  square.     In  the  following  trials  exposures  for  2  minutes  to  the 


EFFICIENCY    OF    FOG    CHAMBER. 


21 


X-ray  bulb,  at  a  distance  of  about  12  cm.  between  the  anticathode  and 
the  glass  wall  (0.3  cm.  thick)  of  the  fog  chamber,  are  in  question.  The 
earthed  iron  plate  was  placed  between  bulb  and  chamber,  resting  on  the 
latter.  A  lapse  of  time  of  1  minute  was  allowed  after  the  radiation  had 
been  cut  off.  This  suffices  to  show  that  nuclei  of  the  persistent  kind 
have  been  entrapped.  Naturally  the  pressure  difference  used  precip- 
itated no  appreciable  fog  in  the  absence  of  radiation. 

These  results  show  conclusively  that  persistent  nuclei  may  be  pro- 
duced through  earthed  tin  plate,  provided  the  thickness  used  is  not 
excessive. 

Table  9. — Persistent  nuclei  through  earthed  tinned  iron  plate,  0.03  cm.  dp*-  25  cm., 
practically  below  fog  limit.  Exposure  to  X-rays,  2  minutes;  lapse,  1  minute;  obser- 
vation during  exposure. 


X-rays — 

s. 

n  X  10-3. 

On 

Off 

On 

2.0 

.0 

2.0 

1Weak 

2-5 

.0 

25 
.0 

Off 

On 

{dp=  24.5;  corona  too  faint  for  measurement,  but  definitely  present. 


16.  Discussion. — The  simplest  of  the  graphs  are  those  of  figure  18, 
showing  the  decrease  of  persistent  nuclei  as  the  bulb  is  gradually  removed 
(D  increasing  and  measured  from  the  side  of  the  chamber)  from  the 
apparatus.  This  decrease  is  very  rapid  and  implies  that  if  the  anti- 
cathode  were  actually  in  contact  with  the  glass  walls  the  production 
of  persistent  nuclei  in  2  minutes  would  be  enormous.  The  distortion 
of  the  coronas  resulting  under  these  circumstances,  as  detailed  in  the 
last  memoir,  is  not,  therefore,  surprising.  It  should  be  remembered  that 
the  rays  have  to  penetrate  more  than  2  mm.  of  glass.  On  the  whole 
the  action  is  very  much  like  what  C.  T.  R.  Wilson  describes  for  ultra- 
violet light. 

As  in  the  earlier  case,  there  is  secondary  generation;  i.e.,  the  number  of 
nuclei  is  larger  if  the  observations  are  made  at  1  or  2  minutes  or  more 
after  the  radiation  has  been  cut  off. 

With  the  given  apparatus,  persistent  nuclei  were  still  produced  for  a 
distance  of  0.5  meter  between  the  X-ray  bulb  and  fog  chamber,  though 
the  coronas  in  that  case  were  but  just  discernible  and  vanished  too 
rapidly  for  measurement.     The  corresponding  intensity  of  ionization 


22  VAPOR    NUCLEI    AND    IONS. 

is  then  near  the  point  of  transition  from  persistent  to  fleeting  nuclei, 
a  result  which  will  presently  be  made  use  of. 

The  pressure  difference  (dp  =  18  cm.)  used  throughout  is  (for  the  given 
apparatus)  far  below  the  fog  limit  for  dust-free  air  (dp  =  21  to  26). 

In  case  of  the  fleeting  nuclei  or  ions,  the  generation  is  instantaneous 
and  it  will  be  necessary  to  represent  the  data  (s,  n,  N)  for  a  continuous 
series  of  supersaturations  for  each  of  the  five  intensities  of  ionization 
applied,  beginning  with  non-energized  dust-free  air.  These  are  given 
for  both  increasing  and  decreasing  values  of  dp,  the  latter  being  at  times 
larger  (as  would  be  expected  from  the  removal  of  larger  groups  on  con- 
densation) ;  but  on  the  whole  the  data  are  very  satisfactory. 

Remembering  that  the  number  is  roughly  as  the  cube  root  of  s,  the 
region  of  ions  (dp  =  21  to  26)  is  particularly  well  represented.  They 
increase  slowly  but  regularly  in  number  until  the  coronal  stages  are 
reached.  Beyond  these  the  increase  is  again  slow;  but  that  it  is  real  is 
shown  by  the  top  curve  for  X-ray  nuclei,  which  fails  to  ascend. 

The  lowest  pressure  at  which  the  suggestion  of  a  corona  could  be 
observed  in  the  given  apparatus  was  dp  =  21  cm.  The  coronal  fog  limit 
is  best  found  from  the  other  curves. 

The  succeeding  curves  (X-ray,  D  =  600;  radium,  D=o;  X-ray,  .D  =  ioo, 
50,  25  from  end  and  50  cm.  from  side)  correspond  to  gradually  increasing 
ionization.  It  may  be  noticed  that  the  fog  limits  slowly  move  to  the 
left  into  smaller  supersaturations,  while  the  initial  slope  of  the  curves 
gradually  rises.  Persistence  sets  in  when  the  slope  is  nearest  the 
vertical.  All  the  curves  eventually  approach  a  limit,  which  for  weak 
radiation  is  practically  reached  near  the  fog  limit  of  air,  but  for  strong 
radiation  much  beyond  it.  In  the  upper  curves  the  green-blue-purple 
corona  first  appears  at  dp  =  30  cm.  It  is  noteworthy  that  the  asymptote 
is  reached  later  as  the  ionization  is  stronger. 

The  relation  of  these  results  as  to  numbers  of  nuclei  is  best  shown  by 
the  w-curves,  fig.  16,  though  the  scale  is  now  too  small  for  the  ions  of 
non-energized  air.  In  this  case  (n)  it  is  assumed  that  the  nuclei  are 
reproduced  faster  than  they  can  be  removed  by  expansion.  The 
curves  throughout  have  the  same  characteristic,  being  doubly  inflected 
and  showing  definite  stages  in  which  nucleation  increases  most  rapidly. 
If  these  branches  are  prolonged  backwards  the  coronal  fog  limit  may  be 
specified  for  each,  as  shown  in  the  figures.  This  quantity  decreases  at  a 
retarded  rate,  while  the  ionization  grows  more  intense. 

The  effect  of  weak  ionization  (radium,  or  X-ray  at  D  =  6oo)  is  to 
increase  the  number  of  ions.  It  has  been  supposed  above  that  the 
result  of  this  is  to  mask  the  corresponding  increase  of  any  of  the  col- 
loidal nuclei  originally  present,  should  such  an  increase  occur. 


EFFICIENCY    OF    FOG    CHAMBER.  23 

The  curves,  moreover,  throw  important  light  on  the  distance  effect 
D.  Thus  at  dp  =  22,  the  effect  of  increasing  D  from  1  to  6  meters  is  a 
fall  of  n  from  50,000  to  20,000 — about  60  per  cent.  At  dp  =  30  the  fall 
is  from  130,000  to  40,000 — about  69  per  cent.  Owing  to  the  uncertain- 
ties of  observation  these  numbers  may  possibly  be  the  same,  in  which 
case  the  gradation  of  size  of  the  nuclei  would  be  the  same  for  all  inten- 
sities of  ionization. 

The  initially  slow  increase  of  the  upper  curves  (D  =  5o  cm.)  is  possibly 
due  to  the  formation  of  persistent  nuclei,  as  stated  at  the  beginning  of 
this  section,  these  capturing  much  of  the  moisture. 

Finally,  the  evidence  given  by  the  N  curves,  fig.  1 7  (assuming  that  the 
nucleation  is  not  restored  faster  than  it  can  be  removed  by  the  exhaus- 
tions), is  much  the  same  as  that  just  detailed.  The  curves  are  often 
straighter  than  heretofore,  and  continually  rise  as  the  result  of  the  in- 
creasing volume  expansion;  but  the  double  inflection  remains.  In  fact, 
the  rise  of  all  the  upper  curves  is  eventually  at  about  the  same  rate  as 
for  air.  In  the  latter  case  the  scale  is  again  too  small  to  show  the  in- 
crease in  the  region  of  ions. 

At  dp  =  22  the  distance  effect  for  1  and  6  meters  is  a  decrease  of  60 
per  cent,  at  ^  =  30  a  decrease  of  71  per  cent,  naturally  nearly  the  same 
as  above. 

Both  the  N  and  n  curves  show  that  while  within  the  limits  of  observa- 
tion intense  radiation  increases  the  nucleation  of  dust-free  air,  this  is  not 
the  case  for  weak  ionization.  Here  the  curves  cross  at  about  dp  —  29  cm. 
Above  this  the  presence  of  radiation  must  decrease  the  efficient  nuclea- 
tion of  non-energized  dust-free  air;  below  this  it  will  increase  it.  At 
high  pressure  differences  like  dp  =  41  cm.,  as  used  below,  the  variation  of 
the  efficient  nucleation  must  therefore  be  a  sensitive  criterion  for  the 
variation  of  the  ionization  of  air.  Similarly  the  direct  experiments  of  sec- 
tions 7  and  9  find  their  explanation  in  the  manner  already  pointed  out. 

17.  More  rapid  exhaustion.  Apparatus  and  data. — The  preceding 
set  of  experiments  correspond  to  the  particular  exhaustion  cock  used. 
This  was  an  inch  plug  gas  cock.  As  almost  the  whole  resistance  to  flow 
was  encountered  here,  the  advisability  of  enlarging  it  seemed  evident. 
In  fact,  on  opening  the  cock  suddenly  to  an  amount  corresponding 
respectively  to  about  1/4,  1/2,  3/4,  i/i,the  nucleations  obtained  were 
about  iVXio~3  =  4o,  100,  180,  350  for  dp  =  ^i  cm.,  showing  that  not 
even  an  approach  to  the  limit  is  reached  in  the  extreme  case.  There  is 
a  further  objection  in  having  the  large  resistance  in  the  stopcock,  as  the 
coronas  will  vary  with  the  degree  of  opening. 


24 


VAPOR    NUCLEI    AND    IONS. 


Table  io. — Nucleation  of  dust-free  air,  energized  or  not.  New  apparatus,  i^-inch 
stopcock;  connections  of  inch  gas  pipe.  Barometer  76.23  cm.  Walls  of  fog  cham- 
ber 0.3  cm.  thick.     Three  horizontal  wet  cloth  partitions  within  chamber. 


dp. 

s. 

n  x  10-3. 

N  x  io-3. 

A*            l 

dp.                   S. 

»XioJ. 

iVxio-3. 

I. 

Ill  (continued).    X-rays.    D=5ocm. 
from  side. 

44 

»77 

180 

440 

42 

x7 

6 

i75 

400 

35-2 

59.o 

240 

45o 

7 

6 

i75 

400 

30.8 

59-3 

258 

440 

7 

6 

i75 

400 

26.6 

59.2 

229 

360 

35 

'7 

6 

160 

300 

22.8 

38.o 

r37 

200 

7 

6 

160 

300 

21.5 

37-3 

120 

170 

30.8 

27 

5 

i37 

235 

20.8 

67-2 

100 

138 

26.1 

2 

6 

62 

9-7 

19-5 

5-i 

39 

52 

24-3 

7 

.  2 

•4 

18.6 

1 . 1 

1 

5 

.  1 

.2 

18.3 

?o 

?o 

?o 

25-3 
26.1 

1 
2 

4 
6 

I.-7 

6.2 

2.6 
9-7 

27.0 

3 

6 

17 

27-5 

27.6 

5 

0 

46 

75 

IV.  X-rays.      D  =  1 2  cm.  from  side. 

28.6 
29-3 

5 
6 

4 
3 

60 
92 

99 

153 

30- 5 

7 

0 

I25 

212 

35 .0 

x7 

7 

160 

300 

18.9 

2 

2 

2.7 

3-7 

35-o 
30.5 

27 

8 
5 

160 
136 

300 
230 

20.0 
21 .0 
23.0 
24-5 

5 
37 
77 
59 

7 
4 
3 
5 

54 
117 

125 
195 

74 
165 
180 
290 

II.  Rad 

ium  tube  2 

idded  on  side.   Barome- 

29-3 

8IO 

5 

290 

490 

35° 

8IO 

7 

320 

610 

tet 

76 .  05  cm 

.    (Mean  values.) 

43-7 

5IO 

3 

306 

750 

52.2 

*9 

4. 

240 

760 

43-6 

4.4 

40 

95 

35-o 

5 

4 

67 

126 

30.8 

5 

6 

69 

120 

V.  Dust-free  air.     Fog  chamber  with  4- 

26.4 
24.2 
22.8 

5 
5 
5 

6 
6 
6 

64 
60 

57 

97 
87 
87 

sheeted  wet  cloth.     2  to  3  cm.  apart. 
Barometer  76.36  cm. 

21 . 2 
20.0 

5 
4 

6 

1 

55 
20 

74 
28 

18.8 

0 

0 

0 

28.8 

5-1 

19.0 

0 

0 

0 

27.0 

3 

4 

19.0 
19.6 

•5 
2.6 

.  1 

5-2 

6.*9 

25-3 
25.8 

2 

0 

1 

20.4 

4-9 

37 

5i 

25.3 

? 

0 

21 .0 

5-2 

43 

60 

25.8 

2 

3 

III.  3 

C-rays.     L 

)  =  50  cm.  from  side. 

30.8 
31.6 

2 
2 

87 
87 

1 
3 
3 

4 

i 

32.3 

(6) 

48.9 

37-6 

190 

560 

33- 1 

67 

7 

43-6 

48.o 

216 

530 

34-o 

97 

8 

g'  BP  corona  steadily  repeated,  but  not  quite  clear. 


*wr  g. 


>wyg. 


'gyog'. 


!wog.  3GBP. 

8wog'. 


*  w  P  corona. 
8  Vague. 


EFFICIENCY    OF    FOG    CHAMBER.  25 

Accordingly  the  inch  stopcock  was  replaced  by  a  ij-inch  plug  gas 
cock,  retaining  the  same  inch  tubing.  The  resistance  in  this  case 
was  least  at  the  stopcock,  which  accounts  for  the  remarkable  steadi- 
ness of  the  results  obtained  in  successive  exhaustions. 

Furthermore,  the  fog  chamber  was  modified  by  inserting  three  wet 
cloth  partitions,  horizontal  and  about  5  cm.  apart,  as  shown  in  fig.  3. 
The  new  form  was  not  merely  favorable  to  better  saturation,  but  all  con- 
vection currents  were  more  effectually  cut  off.  This  was  at  first  (though 
incorrectly)  supposed  to  be  the  reason  for  the  appearance  of  distribu- 
tions of  nuclei  within  the  chamber  produced  by  the  action  of  radium  kept 
outside  of  it,  a  result  already  detailed  above,  but  which  here  appeared 
for  the  first  time  in  a  very  marked  degree.  In  the  later  experiments 
four  cloth  partitions  were  inserted,  as  in  fig.  4. 

The  results  are  given  in  the  successive  parts,  table  10,  in  the  usual 
way,  dust-free  air  being  examined  with  and  without  the  interference 
of  external  radiation.  It  is  not  probable  that  any  errors  are  now  intro- 
duced by  the  filter. 

In  view  of  the  intense  ionization  used,  the  usual  cycle  of  measurable 
coronas  is  exceeded,  and  the  resulting  data  become  more  and  more 
fully  relative,  both  on  this  account  and  because  of  the  high  pressure 
differences  applied.  Absolute  values  are,  however,  of  little  interest,  and 
it  is  precisely  from  the  relations  obtained  that  conclusions  are  to  be 
drawn.  The  quantities  s,  n,  N,  dp  have  been  frequently  defined.  D 
is  measured  from  the  side  of  the  apparatus,  so  that  all  action  takes  place 
through  0.3  cm.  of  glass.     No  aluminum  screen  was  interposed. 

18.  Remarks  on  the  s=curves.  Non-energized  air. — The  present 
5-curves  for  non-energized  air,  fig.  19,  are  in  strong  contrast  with  the 
preceding.  Variability  in  the  lapse  of  time  has  been  nearly  eliminated. 
The  curves  have  moved  bodily  somewhat  farther  to  the  left  into  the 
region  of  smaller  super  saturations,  as  is  shown  by  comparison  with  the 
dotted  line  in  fig.  19  (taken  from  the  preceding  fig.  15),  evidencing  the 
increase  of  efficiency  referred  to.  The  curves  of  fig.  19  are  in  remarkable 
contrast  with  the  preceding  in  two  respects;  they  reach  a  definite 
asymptote  at  about  dp  =  35,  which  is  retained  until  the  pressure  difference 
is  so  high  that  other  complications  step  in.  There  is  certainly  an  incre- 
ment after  dp  =  30,  as  proved  by  the  change  of  coronas.  Whether  this 
limit  is  due  to  a  cessation  of  further  drop  of  temperature  in  the  appara- 
tus, or  whether  a  distinct  group  of  colloidal  air  nuclei  is  in  question, 
remains  to  be  seen.  The  possibility  of  the  continued  succession  of 
groups  of  this  kind  is  not,  a  priori,  improbable. 


26 


VAPOR    NUCLEI    AND    IONS. 


19.  The  same,  continued. — The  other  characteristic,  which  was 
entirely  unforeseen,  is  the  relative  absence  in  what  has  been  called  the 
ionized  region  (placed  in  the  former  curves,  fig.  15,  between  about  dp  =  21 
and  dp  =  26).  The  contrast  is  clearly  shown  in  fig.  19.  The  only  ex- 
planation which  suggests  itself  to  me  is  this,  that  what  were  supposed 
to  be  ions  were  really  water  nuclei  due  to  the  somewhat  slower  exhaus- 
tion of  the  preceding  experiment.  In  other  words,  particles  caught  at 
the  end  of  the  somewhat  less  rapid  expansion  evaporated  into  the  larger 
particles,  leaving  water  nuclei  behind.  But  apart  from  this,  the  definite 
trend  with  which  the  curve  reaches  the  abscissa  is  characteristic,  and,  so 
far  as  coronas  go,  there  seems  to  be  an  absence  of  nuclei  below  dp  =  24. 
In  other  words,  the  fog  limit  has  been  raised,  in  spite  of  the  general  lower- 
ing of  the  necessary  supersaturations  throughout  the  curve.  The  new 
curve  is  almost  wholly  coronal. 


WOff' 


wPcor 


ZO  ZZ  24  Z6  ZB  30  32  34  36 

Fig.  19. — Improved  fog  chamber.  Apertures  of  coronas  (s)  seen  in  dust-free  air, 
energized  or  not,  as  stated,  by  radium  or  X-rays,  at  different  exhaustions  (dp). 
Table  10. 


Usually  the  same  results  are  obtained  in  a  pressure-increasing  and  in 
a  pressure-decreasing  series.  There  is  an  equally  striking  uniformity 
in  the  lapse  of  time. 


EFFICIENCY    OF    FOG    CHAMBER.  27 

20.  The  same,  continued.  Action  of  radium. — The  action  of  radium 
is  characterized  by  a  slight  rise  of  the  asymptote  over  the  preceding 
case  and  of  displacement  of  the  curve  into  smaller  supersaturations. 
This  was  to  be  anticipated;  nuclei  are  caught  more  easily,  and  a  some- 
what smaller  order  of  size  and  increased  number  is  detected  in  conse- 
quence. The  other  distinctive  feature  is  the  smaller  range  of  pressure 
differences  within  which  practically  all  condensation  occurs.  In  the 
preceding  experiments  this  range  lay  between  dp  =  18  and  24,  whereas  in 
the  present  case  the  marked  changes  fall  between  dp  =  ig  and  2 1 .  There 
results  another  apparent  rise  of  the  fog  limit  corresponding  to  the  coronal 
effects,  though  it  is  slight  and  uncertain.  What  is  noteworthy  is  the 
greater  steepness  of  the  rising  branch  of  the  curve,  already  indicated. 
The  question  may  be  asked  whether  for  a  rigorously  instantaneous 
exhaustion  this  part  of  the  curve  would  become  even  more  nearly 
vertical.  One  may  note  that  the  radium  curve  eventually  passes 
through  a  maximum.  Furthermore,  while  in  its  initial  stages  it  lies 
very  near  the  former  X-ray  curve  (D  =  $o),  the  latter  shows  no  tendency 
to  reach  a  near  asymptote. 

21.  The  same.  Action  of  X=rays. — Finally,  the  results  with  the 
X-rays  are  similar.  High  asymptotes,  a  tendency  of  the  curve  to  lie 
within  a  region  of  lower  supersaturations  than  in  table  7,  etc.,  are 
apparent.  Nuclei  smaller  in  size  and  larger  in  number  have  been  caught 
more  easily  than  heretofore.  If  we  regard  the  present  and  the  earlier 
curves  for  D  =  5o,  the  height  of  asymptote  in  the  former  case  is  much 
above  the  one  in  the  latter  case,  and  moreover  passes  through  the 
maximum  (reached  at  dp  =  26)  as  dp  increases  indefinitely.  This  cor- 
responds to  the  result  for  radium. 

It  is  therefore  interesting  that  if  the  radiation  is  further  intensified, 
as  in  the  last  case,  where  D  =  1 2  cm. ,  the  curve  continues  to  rise  apparently 
throughout  higher  ranges  of  pressure.  The  limits  are  not  reached  (dp 
continually  increasing)  until  nuclei  of  a  size  equal  in  smallness  to  the 
order  holding  for  the  colloidal  nuclei  of  air  have  become  available  for 
condensation.  A  final  point  deserving  comment  is  the  break  of  the 
X-ray  curve  near  dp  =  22.  This  is  not  only  marked  in  both  curves  of 
table  10,  but  similarly  apparent  in  table  7.  Unfortunately,  the  cycle  of 
coronas  changes  at  this  point  (green-blue-purple  corona);  but  apart 
from  this  it  seems  probable  that  with  intense  X-ray  radiation,  two  suc- 
cessive groups  of  nuclei  are  in  question ;  the  first  group  prominent  below 
dp  =  2  2  and  the  second  above  dp  =  22. 

22.  Remarks  on  the  w=curves.  Non=energized  air. — The  w-curves, 
which  assume  that  the  nuclei  are  replaced  sooner  than  they  can  be 


28 


VAPOR    NUCLEI    AND    IONS. 


removed  by  exhaustion,  bring  out  the  points  just  made  with  better 
regard  to  the  actual  nucleation,  seeing  that  the  s -curves  are  specially 
favorable  to  small  numbers  of  nuclei.  As  a  rule  the  new  nucleations 
obtained  are  nearly  twice  as  large  as  the  old  results.  It  seems  probable 
that  the  upper  inflection,  after  passing  the  nearly  straight  part,  is  due 

f 
eeo 


240 


18  20  22  24  26  28  30  32  34  36  38  40 


Fig.  20. — Improved  fog  chamber.     Efficient  nucleation  (n)  free  air  cor- 
responding to  fig.  19.     Table  10. 

to  the  waning  condensing  power  of  the  apparatus,  and  that  in  the 
absence  of  this  loss  of  efficiency  the  middle  region  of  the  doubly  inflected 
curve  would  continue  indefinitely.  One  may  note,  too,  that  both  in  case 
of  tables  7  and  10  the  parts  in  question  are  nearly  parallel,  or  that  the 
increment  of  nucleation  corresponding  to  a  given  increment  of  super- 


EFFICIENCY    OF    FOG    CHAMBER. 


29 


saturation  is  about  the  same.  This  applies  even  in  the  following  cases, 
where  dust-free  air  is  energized  by  radium  and  by  intense  X-radiation, 
as  far  as  the  middle  regions  of  the  curve  are  concerned. 

23.  The  same.  Action  of  radium. — The  small  increment  of  pressure 
difference  (say  dp  =  19  to  21)  is  here  in  sharp  contrast  to  the  gradual 
increase  observed  in  the  old  results  (say  between  dp  =  19  and  25).  The 
nucleations  which  eventually  are  not  quite  doubled  in  the  new  results, 
as  compared  with  the  older,  are  therefore  at  first  enormously  in  excess. 
In  fig.  20  the  results  of  table  10  are  given  in  full,  the  old  results  (table  7) 
in  broken  lines,  and  the  same  method  is  pursued  in  the  other  cases. 


300 


22  24  26  28  30  32  34  36  38  40  42 

Fig.  2i. — Efficient  nucleation  (N)  in  dust-free  air  corresponding  to  fig.  19.     Table  10. 

24.  The  same.  Action  of  X=rays. — Remarks  to  the  same  effect  may 
be  made  with  reference  to  the  old  and  the  new  data  for  X-ray  ionization 
when  D  =  $o  (broken  and  full  lines  in  fig.  20).  Initially  the  old  curve 
is  even  below  the  present  curve  for  radium,  but  it  eventually  intersects 
the  new  data  for  dust-free  air  at  about  dp  =  3  5 .  The  mean  nucleations 
have  not  been  quite  doubled.  The  maxima  in  cases  of  D  =  50  and  D  =  1 2 
lie  above  the  interval  of  large  variation  for  dust-free  air.  Finally,  the 
breaks  in  the  curves  at  dp  =  22  are  again  quite  apparent. 

25.  Remarks  on  the  Ar=curves. — With  regard  to  the  iV-curves,  fig.  21, 
one  need  merely  note  that  the  maxima  have  in  most  cases  been  defi- 
nitely wiped  out,  and  that  the  nucleation  available  for  condensation,  if 
it  be  supposed  that  removal  of  nuclei  is  more  rapid  than  the  reproduction, 
increases  continually  with  the  supersaturation  up  to  the  highest  values. 


30  VAPOR    NUCLEI    AND    IONS. 

THE  NUCLEATION  OF  FILTERED  AIR  IN  THE  LAPSE  OF  TIME. 

26.  Method. — In  the  above  experiments  with  filtered  air,  it  has  been 
carefully  pointed  out  that  all  the  curves  tend  to  reach  asymptotes,  the 
height  of  which  depends  on  the  other  (larger)  nuclei  present.  If,  then, 
the  ionization  of  dust-free  air  is  an  essentially  variable  quantity,  as 
shown  by  the  electrometer,  the  height  of  the  asymptote  in  question 
should  be  correspondingly  variable. 

Again,  it  was  shown  that  external  radiation  (gamma-rays  of  radium 
for  instance)  are  powerful  nucleators,  whether  directly  or  secondarily. 
Hence  external  radiation  of  this  type,  if  variable,  might  be  reasonably 
sought  for  in  a  study  of  the  nucleation  of  dust-free  air. 

In  relation  to  the  ordinary  intensities  of  radiation,  this  method  of 
varying  asymptotes  is  exceedingly  sensitive.  Whether,  however,  it 
will  apply  for  cases  of  much  weaker  (cosmical)  radiation  must  be  left 
to  experiment.  Moreover,  whether  the  variable  ionization  of  air  can  be 
detected  in  the  manner  suggested,  or  whether  it  even  exists  in  the  fog 
chamber,  is  similarly  a  question  requiring  experimental  solution. 

27.  Early  data. — The  method  here  in  question  was  carried  out  in  a 
series  of  experiments  begun  May  9  and  continued  until  September  2, 
1905.  In  the  earlier  part  of  the  work  it  was  shown  that  comparable 
results  could  only  be  expected  in  cases  of  excessively  slow  filtration, 
the  filters  for  this  purpose  being  18  inches  long,  2  inches  or  more  in 
diameter,  and  containing  cotton  very  tightly  packed.  It  was  necessary, 
moreover,  to  make  observations  after  long  intervals  (12  to  24  hours)  of 
waiting,  the  object  being  to  allow  all  nuclei  which  might  have  passed 
through  the  filter  time  to  decay.  Apparent  variations  of  considerable 
interest  were  obtained  in  this  way ;  but  the  work  below  will  show  them 
to  have  been  untrustworthy.  Neither  changes  of  temperature  nor  of 
the  barometer  produced  any  effect. 

To  additionally  safeguard  the  work,  two  fog  chambers  were  eventually 
installed  side  by  side,  drawn  upon  by  the  same  exhaustion  system 
identically  in  every  way.  It  was  then  found  that  the  internal  partitions 
of  wet  cloth  were  essential,  but  it  was  nevertheless  impossible  to  make 
both  chambers  agree  even  when  the  partitions  were  increased  four- 
fold. Throughout  the  work,  nucleations  passing  through  maxima  and 
minima  within  the  limits  of  about  400,000  and  160,000  were  obtained, 
apparently  under  trustworthy  conditions.  The  data  remained  consistent 
even  when  the  fog  chambers  were  exchanged.  Small  variations  of  the 
rate  of  filtration  were  quite  ineffective,  showing  that  a  limit  has  been 
reached. 


NUCLEATION    IN    LAPSE    OF   TIME. 


31 


28.  Apparatus  modified. — The  tubing  of  the  preceding  apparatus, 
which  consisted  of  inch  plug  cock  and  inch  gas  pipe,  was  now  taken  apart 
and  a  1  J-inch  brass  plug  cock  was  substituted.  The  advantage  of  this 
arrangement  is  easily  seen,  inasmuch  as  the  whole  resistance  to  flow  is 
practically  in  the  pipes.  The  passage-way  in  the  stopcock  being  larger 
in  area,  the  rate  of  exhaustion  obtained  is  independent  of  slight  differences 
in  opening. 

As  a  result  of  this,  all  the  variations  noted  above  practically  disap- 
peared, and  the  nucleations  of  dust-free  air  at  a  given  pressure  difference 
were  found  to  be  constant  in  the  lapse  of  time  within  the  limits  of 
accuracy  of  the  method.  Data  of  this  character  are  shown  in  the 
following  table : 


Table  11. — Nucleation  in  the  lapse  of  time.      dp  =30.6  cm.      wo  g' 

iVXlO-3=227. 


nxio- 


127; 


Date. 

Corona. 

s. 

Date. 

Corona. 

s. 

Sept.  51 

wog 

7-4 

Sept.  12 

wog 

6 

wog 

7 

4 

13 

wog 

7 

7 

wog 

7 

4 

14 

wog 

7.2 

8 

wog 

7 

4 

15 

wog 

7 

9 

wog 

7 

4 

16 

wog3 

7-1 

9J 

wog 

7 

3 

18 

wog 

7.2 

10 

wy'g 

7 

4 

20 

wog 

11 

wog? 

21 

wog 

7.2 

1  Apparatus  with  three  sheets. 

1  Apparatus  with  four  sheets. 

8  Apparatus  with  one  sheet,  10  cm.  above  surface  of  water. 


Indeed,  the  succession  of  different  fog  chambers  with  1,2,  and  3  cloth 
partitions  all  gave  the  same  results.  The  rate  of  filtration  could  be 
varied  without  effect  within  wide  limits,  and  the  same  corona  was 
obtained  after  a  few  minutes  or  after  24  hours  of  waiting. 


29.  Inferences. — It  has,  therefore,  not  been  possible  to  detect  changes 
of  nucleation,  either  as  the  result  of  the  concomitant  changes  of  atmos- 
pheric ionization  or  as  the  possible  result  of  some  form  of  cosmical  or 
at  least  external  radiation.  The  consistency  of  the  results  obtained  for 
radiation  under  widely  different  conditions  may  be  especially  pointed 
out.  It  does  not  follow,  however,  that  other  methods  (not  depending 
on  the  terminal  asymptote)  may  not  be  more  efficient.  In  how  far  this 
is  the  case  will  be  shown  in  Chapter  VI. 


32  VAPOR    NUCLEI    AND    IONS. 


SUMMARY  OF  THE  RESULTS  OF  THE  CHAPTER. 

30.  Distribution  of  ions  within  the  fog  chamber. — Within  the  fog 
chamber,  the  coronas  due  to  the  ions  produced  either  by  radium  or 
by  the  X-rays  acting  axially  from  long  distances,  as  a  rule  vary  in 
aperture  from  one  end  of  the  long  vessel  to  the  other.  Hence  the 
distribution  of  nuclei  is  not  uniform  in  the  direction  of  the  axis  of  the 
fog  chamber.  The  reason  for  this  is  to  be  ascribed  to  secondary  radia- 
tion. As  interpreted  from  the  nucleation  produced  within  the  fog 
chamber  containing  dust-free  moist  air,  dense  bodies  (brass  cap)  produce 
more  secondary  radiation  than  rare  bodies  (glass  end)  under  like  con- 
ditions of  primary  radiation. 

If  the  primary  radiation  is  relatively  intense,  rare  bodies  like  glass 
may  produce  more  secondary  radiation  than  dense  bodies  (like  the 
metals)  under  less  intense  primary  radiation;  or  at  least  the  decrement 
of  primary  radiation  with  the  distance  from  the  source  predominates 
within  the  fog  chamber. 

The  secondary  radiation  is  rapidly  absorbed  by  the  air,  as  the  dimin- 
ishing coronas  testify. 

31.  Minimum  of  efficient  nucleation. — When  ions  and  colloidal  nuclei 
are  in  presence  of  each  other  (or  in  general  any  two  groups  of  nuclei  of 
different  average  size),  the  number  of  efficient  nuclei  for  the  case  of  a 
drop  of  pressure  not  too  small  passes  through  a  well-defined  minimum, 
if  the  number  of  ions  continually  increases  from  zero.  This  occurs,  for 
instance,  when  a  radium  tube  is  moved  from  a  long  distance  quite  up  to 
the  fog  chamber.  The  ions  abstract  more  and  more  of  the  available 
moisture,  until  the  colloidal  nuclei  are  practically  inactive  (minimum), 
after  which  the  nucleation  increases  again  with  the  number  of  ions. 

32.  Persistent  nuclei. — For  the  moderately  intense  X-ray  bulb  (5- 
inch  spark)  and  a  glass  fog  chamber  several  millimeters  thick,  persistent 
nuclei  may  be  demonstrably  produced  when  the  distance  from  bulb  to 
chamber  increases  to  about  50  cm.  They  may  even  be  produced  through 
thin  tin  plate.  The  decrease  with  distance  of  the  number  generated 
within  a  given  time  is  very  rapid,  and  the  number  producible  if  the 
anticathode  could  touch  the  fog  chamber  would  be  enormous.  In  like 
manner  the  number  increases  at  an  accelerated  rate  with  time  of  expos- 
ure as  if  the  nuclei  were  themselves  active. 

If  we  regard  the  ionized  state  of  a  gas  as  characterized  by  a  kind  of 
kinetic  ionization  pressure,  we  may  further  conceive  the  ionized  gas  to 


NUCLEATION    IN    LAPSE    OF    TIME.  33 

be  subject  to  something  resembling  saturation,  whereby  ions  pass  into 
persistent  nuclei  when  the  ionization  pressure  reaches  a  certain  limit 
very  much  as  a  vapor  condenses. 

33.  Dependence  of  efficiency  of  fog  chamber  on  the  size  of  the  exhaust 
pipes. — If  a  (long)  cylindrical  fog  chamber,  whose  contents  are  not 
much  in  excess  of  6,000  c.  cm.,  be  exhausted  into  a  vacuum  chamber 
whose  contents  exceed  100,000  c.  cm.,  through  a  passage-way  50  cm.  in 
length  and  about  2.5  cm.  in  bore,  many  of  the  experiments  showing 
the  properties  of  ions  and  of  the  colloidal  nuclei  of  dust-free  air  are  con- 
sistently producible,  provided  the  plug  exhaustion  stopcock  (opened 
quite  and  as  quickly  as  possible)  has  a  wider  bore  than  the  pipes.  With 
exhaust  pipes  of  this  size,  however,  the  apparatus  is  as  yet  very  far 
from  its  limits  of  efficiency,  and  the  largest  or  terminal  corona  obtainable 
in  case  of  the  colloidal  nucleation  of  dust-free  air  is,  even  at  the  highest 
exhaustion,  the  intermediate  green-blue-purple  type.  This  leaves  the 
whole  order  of  large  coronas  outstanding,  though  the  order  may  be 
entered  if  the  air  is  intensely  ionized.  It  follows  that  efficiency  actually 
stops  short  because  of  the  smallness  of  the  colloidal  nuclei. 

The  curves  showing  the  nucleation  entrapped  in  case  of  continually 
increasing  exhaustion  all  have  a  common  feature;  there  is  an  initial 
low  branch  of  small  variation  attributable  to  ions;  an  intermediate 
branch  showing  steep  ascent,  due  to  colloidal  nuclei;  a  final  asymptotic 
branch,  corresponding  to  the  terminal  corona  and  due  to  the  loss  of 
efficiency  of  the  apparatus.  The  middle  branch  in  question,  or  line  of 
representative  colloidal  nuclei,  if  it  appears  at  all,  has  almost  the  same 
slope  and  position  (relative  to  the  field  as  a  whole)  for  all  fog  chambers, 
whether  their  efficiency  be  small  or  great.  The  fog  chamber  ceases  to 
act  almost  abruptly;  in  other  words,  the  terminal  corona  or  largest 
corona  producible  as  the  drop  of  pressure  continually  increases,  appears 
in  any  fog  chamber  as  an  almost  sudden  departure  from  the  representa- 
tive lines.  This  corona  is  larger  or  smaller,  the  asymptote  higher  or 
lower,  as  the  fog  chamber  is  more  or  less  efficient. 

34.  Invariable  character  of  colloidal  nucleation  in  the  lapse  of  time. — 

The  terminal  corona  (in  a  given  type  of  apparatus),  if  not  too  small 
(Chapter  VI),  is  a  fixture  as  to  size  in  the  lapse  of  time  (months).  It 
does  not  vary  appreciably  with  the  departure  from  normal  ionization, 
to  which  atmospheric  air  is  incident.  Probably  the  number  of  available 
colloidal  nuclei  is  too  enormous,  as  compared  with  the  small  variations 
in  number  of  the  relatively  large  ions,  to  admit  of  an  observable  effect. 


CHAPTER  II. 

LATER  AND  FINAL  STAGES  IN  THE  EFFICIENCY  OF  THE  FOG  CHAMBER 
DUE  TO  A  GRADUAL  INCREASE  IN  THE  BORE  OF  THE  EXHAUST  PIPES. 

CONNECTING  PIPES  NOT  LARGER  THAN  1.5   INCHES   IN   DIAMETER. 

35.  Introductory. — It  will  be  the  object  of  the  present  chapter  to 
further  determine  to  what  an  extent  a  perfectly  efficient  apparatus 
(i.  e.,  one  in  which  the  cooling  and  the  moisture  precipitated  per  cubic 
centimeter  actually  accords  with  the  drop  in  pressure)  may  be  ap- 
proached by  gradually  enlarging  the  bore  of  the  escape  pipes  between  the 
vacuum  chamber  and  the  fog  chamber.  One  method  of  doing  this  will 
consist  in  finding  whether  the  distribution  curves  eventually  reach  a 
fixed  limit  and  a  limit  maintained  for  larger  as  well  as  smaller  nuclei; 
another  by  comparing  the  final  results  with  corresponding  data  deduced 
for  Wilson 's  piston  apparatus. 

In  treating  the  large  numbers  of  observations  which  follow,  it  will  be 
convenient  to  refer  the  nucleations  (as  above)  to  the  drop  of  pressure 
observed  under  apparently  isothermal  conditions  at  the  fog  chamber. 
This  method  of  comparison  is  sufficient  if  the  same  fog  and  vacuum 
chambers  are  used  throughout,  as  has  actually  been  done  in  the  sequel. 
The  exhaust  cock  is  always  to  be  closed  immediately  after  exhaustion. 
In  the  present  experiments  the  volume  ratio  of  the  two  vessels  was  about 
v/V  =  0.064,  where  v  is  the  volume  of  the  fog  chamber  and  V  that  of  the 
vacuum  chamber. 

It  was  customary,  as  just  stated,  to  open  the  stopcock  between  the 
fog  chamber  and  the  vacuum  chamber  as  rapidly  as  possible  and  then 
to  close  it  at  once ;  dp  therefore  denotes  the  drop  of  pressure  read  off  on 
the  mercury  gage  at  the  fog  chamber  after  sufficient  waiting.  As  above, 
s  is  the  angular  diameter  of  the  coronas  on  a  goniometer  radius  of  30 
cm.,  when  the  eye  and  the  source  of  light  are  respectively  40  cm.  and 
250  cm.  on  opposite  sides  of  the  fog  chamber.  On  the  basis  of  these 
data  n  is  computed  from  the  quantity*  of  water  precipitated  per  cubic 
centimeter  and  the  value  s,  in  the  way  shown  elsewhere. f  It  is  always 
assumed  that  the  nuclei  are  more  rapidly  reproduced  than  removed  by 
the  exhaustion,  or  (without  hypothesis)  from  another  point  of  view, 

♦Wilson:  Phil.  Trans.  Roy.  Soc.  London,  vol.  189,  1897,  p.  298. 
f  Smithsonian  Contributions,  vol.  xxxiv,  No.  1651,  1905,  chap.  viii. 

34 


EFFICIENCY    OF    FOG    CHAMBER. 


35 


that  the  nucleation  of  the  exhausted  fog  chamber  is  specified.  Otherwise 
it  would  be  necessary  to  multiply  by  the  ratio  of  volumes  after  and  before 
exhaustion. 

Diagrams  of  the  apparatus  used  have  already  been  given  in  Chapter 
II  (figs,  i  to  4),  and  further  examples  will  be  shown  of  the  details  of  the 
more  perfected  forms  below  (figs.  26,  34,  64).  In  those  paragraphs, 
moreover,  I  will  treat  the  corrections  to  be  applied  (which  are  much 
larger  than  were  anticipated)  in  order  to  pass  from  the  observed  appar- 
ent dp  to  the  true  values.  These  must  be  computed  from  the  volume 
ratio  of  the  two  chambers  and  their  respective  initial  and  their  final 
isothermal  pressures  when  in  communication. 

36.  Examples  of  data  for  1-inch  connecting  pipes. — These  were  about 
18  inches  or  more  in  length  and  the  stopcock  inserted  was  i\  inches  in 
bore,  as  specified  in  the  preceding  chapter.  The  plug  was  as  usual 
floated  in  paraffin  oil,  absolutely  preventing  the  influx  of  atmospheric 
air,  though  some  leakage  (which  is  generally  harmless)  from  the  fog 
chamber  to  the  vacuum  chamber  could  not  be  prevented.  The  fog 
chamber  in  these  exhaustions  had  a  rather  larger  charge  of  water  than 
usual,  a  circumstance  to  which  the  higher  fog  limits  may  possibly  be 
due,  since  these  vary  with  the  volume  ratio. 

Table  12. — Pipes  1  inch,  cock  i\  inches.      Non-energized 
dust-free  air.     October  24. 


dp. 

s. 

n  xio-3. 

30.6 

7-4 

139 

28.9 

5-8 

74 

27    2 

4.2 

26 

25-7 

i-5 

i-9 

24.6 

0 

The  results  are  to  be  shown  below  (fig.  22,  p.  37)  in  comparison  with 
the  later  values  and  may  be  passed  over  here. 

37.  Data  for  pipes  1 . 5  inches  in  diameter. — Fog  chamber  and  vacuum 
chamber  were  now  connected  by  brass  gas  pipes  ij  inches  in  diameter 
and  2  feet  long,  and  the  plug  stopcock  interposed  was  2  inches  in  bore. 
In  the  case  of  table  1 3  the  disposition  of  apparatus  was  such  as  to  require 
the  length  of  piping  specified  with  an  elbow.  The  results  are  given  in  the 
usual  way  and  show  a  distinct  gain  in  efficiency  over  the  earlier  set  in 
table  1 3 ,  proving  that  greater  width  of  pipe  is  still  an  advantage. 


36 


VAPOR    NUCLEI    AND    IONS. 


Table  13. — Nucleation  of  dust-free  air,  energized  or  not,  as  stated,  at  different  super- 
saturations.     Plug  gas  cock,  2  inches;  piping  i£  inches  in  bore,  2  feet  long. 


dp. 


ttX  io" 


I.  Non-energized  air. 


cm. 

cm. 

30-7 

x7.2 

28.2 

59 

26.3 

3-7 

24.4 

2.7 

22.4 

2-3 

20.3 

.0 

22.0 

1-7 

24.7 

2.7 

27.6 

6.1 

29.9 

27-3 

34-2 

s8.i 

151 

77 

19.7 
6.8 

3-3 

.0 

2.1 

6.8 

80 

135 
190 


Non-energized  air.  Exper- 
iments. 


.8 

8.4 

•  7 

f  4IO.O 

.8 

I    68-9 

.6 

{  4io-7 

•5 

\    59.o 

190 

270 
220 
270 
220 


II.  Non-energized  air. 


42.1 

e9-3 

34-5 

7io.5 

32.1 

89.  2 

30.0 

B8.o 

27.9 

6.1 

26.0 

3-8 

24-3 

2.7 

22.5 

2.0 

21. 1 

?I.O 

173 

!.o 

18.6 

!.o 

250 

318 

262 

150 
80 

20 
6. 


2.3 

r 
.0 
.0 


nX  io" 


II  (continued).    Non- 
energized  air. 


19.9 

?o.8 

20.4 

I  .2 

21  .O 

1.6 

0.6 

I  .  2 

i-7 


Later. 


43-5 

hi. 2 

47-9 

7II.2 

43-8 

7io.8 

39-1 

8IO.I 

34-9 

108.9 

30.8 

n7-5 

354 
372 
338 
286 
192 
144 


III.  Air  energized  by  radi- 
um, on  side  of  glass  fog 
chamber. 


21.7 

6.0 

20.9 

5-7 

20.  2 

5-2 

18.6 

1.0 

16.5 

.0 

>i8.7 

I  .2 

18.8 

i-9 

21 .0 

?5-7 

20.0 

5-4 

26.4 

6.8 

24.9 

6.8 

23-5 

6.8 

22.0 

6.7 

20.0 

5-4 

29.0 

6-5 

33-2 

6.0 

38.9 

5-9 

43-6 

5-7 

67 
56 
42 

.8 
.0 

?1.2 
2.0 
56 

47 
104 
100 

96 

89 

47 

99 

88 

9i 

85 


dp. 


n  X  io~3. 


IV.  Air  energized  by  X- 
rays12.  D  =  20  cm.  from 
side  of  fog  chamber  to 
anticathode. 


34-7 

l3i2.3 

31.0 

13I2.3 

26.3 

13i2.3 

22.0 

14io.6 

17.6 

1.4 

16.5 

.0 

17.6 

2. 1 

19.6 

158.i 

19.0 

4.4 

400 

380 
340 

207 

I 
o 

2 

I4O 

24 


V.  X-rays.    Z?=5ocm. 


32. 
35< 
26. 
22, 
17 
17' 
19 
20. 


I 

"11.4 

0 

16n.3 

6 

14io.7 

1 

178.6 

4 

?r 

7 

?o 

0 

2.2 

0 

6.1 

310 
320 
233 
145 

o 
o 

2.7 
64 


X-rays.    D  =  20  cm.  after 
long  waiting. 


34-6 


g'  B  p,  repeated.      2gyobg.      s  w  p  cor.      'wvog,   after  waiting  one  or  more  hours.  8w'  P  cor 

after  waiting  but  a  few  (io  to  15)  minutes.    6wcg.    7wog.    8wrg.    9g' B  P.  10wP  cor.  "wycor. 

"Air  non-energized,  ftp—  348;  8=9.6;  and  by  X-rays.     1Jwygr  large,    "wrg.  16w  c  g.  "wobg. 
17  w  P cor.     18gyobg. 

Long  waiting  before  exhaustion  (to  remove  water  nuclei)  is  often 
essential.  In  addition  to  the  dust-free  gas,  air  energized  by  radium  (io 
mg.  of  a  weak  sample,  io,oooX,  sealed  in  aluminum  and  acting  from 
without)  and  by  the  X-rays  is  treated  for  comparison. 


EFFICIENCY    OF    FOG    CHAMBER. 


37 


400 


360 


280 


Z40 


Fig.  22 — Efficient  nucleation  in)  found  in  dust-free  air  energized  or  not  by  radium  or 
the  X-rays,  as  stated,  from  different  distances  (D),  at  different  exhaustions  (dp). 
Fog  chamber  with  pipes  ij-inch  bore,  2  feet  long.     Table  13. 


38  VAPOR    NUCLEI    AND    IONS. 

These  results,  together  with  the  data  of  table  12,  are  shown  in  fig.  22. 
For  the  air  curve  a  marked  advance  beyond  the  results  of  table  1 2  is  at 
once  apparent,  but  it  is  noteworthy  that  the  slopes  of  both  curves  are  in 
the  main  the  same,  in  spite  of  the  fact  that  the  former  rises  to  but  one- 
half  or  one- third  of  the  height  of  the  new  curve.  The  efficiency  of  both 
fog  chambers  therefore  terminates  abruptly  in  a  final  or  fixed  corona  or 
(in  the  chart)  in  an  asymptote  which  would  be  horizontal,  if  it  were  not 
necessary  to  assume  that  the  quantity  of  water,  m,  precipitated  per  cubic 
centimeter  increases  with  the  drop  in  pressure.  In  the  different  series, 
irregularities  are  often  apparent  which  are  difficult  to  explain,  though  at 
low  values  they  may  be  due  to  cosmical  radiation.  Thus  the  second 
series  for  non-energized  air  rises  more  abruptly  than  the  first  and  third, 
results  which  are  possibly  associated  with  the  presence  of  water  nuclei 
and  referable  to  different  degrees  of  leakage  from  fog  chamber  to  vacuum 
chamber;  but  it  is  also  possible  that  unequally  rapid  closing  of  the  stop- 
cock after  exhaustion  may  have  left  an  impression.  The  results  for 
radium  and  the  X-rays  will  reappear  under  better  conditions  presently, 
and  may  then  be  discussed.  One  may  note  that  for  weak  radiation  the 
graphs  intersect  the  graph  for  non-energized  air. 

38.  Continued.  Shorter  pipes. — The  next  step  consisted  in  a  remodel- 
ing of  the  apparatus,  whereby  shorter  connecting  pipes  would  suffice. 
Two  6-inch  nipples,  i£  inches  in  diameter  and  containing  a  2 -inch  plug 
stopcock,  now  joined  the  fog  and  vacuum  chambers.  The  results  are 
shown  in  table  14  and  in  fig.  23.  The  fact  that  the  main  resistance  is  still 
encountered  in  the  gas  cock  is  proved  by  the  need  of  stops  to  insure  quick 
and  complete  opening.  Whenever  the  cock  is  nearly  but  not  quite 
opened,  however  suddenly,  low  coronas  are  observed.  When  this  was 
remedied,  fixed  coronas  thereafter  corresponded  to  each  dp.  The  table 
contains  the  usual  series  of  comparative  results  for  air  energized  by 
radium  and  the  X-rays. 

As  compared  with  the  preceding  data  there  is  a  small  shifting  of  the 
graph  toward  lower  pressures,  while  the  slopes  in  the  representative  parts 
of  the  curves  are  practically  the  same.  The  terminal  corona,  however,  and 
the  corresponding  asymptote,  is  markedly  raised.  Nevertheless,  though 
the  large  green-blue-purple  corona  now  appears  in  the  case  of  strongly 
energized  air,  it  has  not  yet  been  reached  in  the  non-energized  cases. 
The  limit  of  efficiency  is  therefore  not  yet  in  sight  when  a  fog  chamber  of 
about  ^  =  6,000  c.  cm.  empties  into  a  vacuum  chamber  of  about  V  = 
100,000  c.  cm.  through  30  cm.  of  piping  about  4  cm.  in  diameter,  with  a 
corresponding  plug  stopcock  suddenly  opened  between  stops  to  arrest 
the  motion. 


EFFICIENCY    OF    FOG    CHAMBER. 


39 


Table  14. — Nucleation  of  dust-free  air,  energized  or  not,  at  different  supersaturations. 
Plug  gas  cock,  2  inches ;  piping  1  £  inches  in  diameter,  2x6  inches  long.  Long  intervals 
between  observations. 


dp. 


Corona. 


n  Xio" 


I.  Non-energized  air.1 


39.8 

12.8 

39-8 

130 

35-1 

13.0 

30.8 

10.4 

28.6 

7-4 

27.9 

5-7 

26.0 

2.4 

26.4 

3-6 

gyobg 

wybg 

wyg 

wr  g 

wrg 

w  B  P 

cor 

cor 


II.  Non-energized  air.1 


243 

1.5 

24.4 

1.8 

26.2 

2.6 

27.3 

5.o 

28.0 

6.4 

293 

7.6 

295 

8.0 

30.9 

10. 0 

30.4 

8-4 

31.2 

9-i 

350 

"•5 

cor 

cor 

cor 

cor 
wrg 
gBP 
gBP  + 
w  r  o  g 
wcg 
wrg 
wyg" 


III.  Non-energized  air. 


31.0 

9-8 

31.0 

10.3 

310 

2io.4 

35.3 

12.0 

351 

12.0 

39-4 

12.0 

44.1 

12.5 

41-3 

12.5 

38.6 

12.0 

307 

10.2 

w  r  o  g 
wr  og 
wr  og 
wybg 
wybg 
wybg 

gyo 

gyo 

wybg 
wrg 


460 
420 
400 
260 
108 

69 
45 

17 


2 

6 

46 

92 

139 

147 

290 

230 

260 

400 


290 
290 
290 
400 
400 
420 
490 
470 
420 
290 


IV.  X-rays  at  D  =  20  cm.  from  side. 


30.9 

130 

35-4 

130 

33-0 

13.0 

31-5 

13.0 

29.  2 

130 

gBP 
gBP 
gBP 
gBP 
gBP 


460 
480 
470 
460 
430 


dp. 


Corona. 


WXIO" 


IV  (continued).     X-rays  at  Z?=  20  cm. 
from  side. 


27.2 

12.7 

25.6 

12.7 

24.1 

12.2 

22.8 

11. 9 

29.4 

12.3 

27.1 

Vague 

20.8 

7-7 

23-4 

11. 7 

22.9 

11. 4 

21.4 

8.4 

20.2 

4.6 

18.7 

.0 

18.3 

.0 

gyo 
gyo 

wyg' 
wog 
gBP 
gBP 

wog 

wog 

gBP 

cor 


380 

360 

320 

250 

440 

410 

120 

250 

250 

120 

30 

o 

o 


IV.  X-rays.     D  =  10  cm. 


351 

14 

0 

40- 3 

37-9 

33-6 

31-6 

30.0 

28.1 

26.7 

25.0 

13 

5 

23.6 

12 

6 

22.3 

10 

3 

21.2 

7 

1 

20.1 

4 

2 

18.7 

1 

3 

3gB 

gB 


gB 
gB 
gB 
gB 
gB 
gB 
4gB 

gyo 

wog 

wog 

cor 


480 
5io 
500 
470 
460 
450 
430 
410 
400 
320 
250 
100 
21 
1-3 


V.  Air8  energized  by  radium,  D 
side. 


o,  on 


30- 8 

6.1 

35-2 

6.2 

40.0 

59 

27.6 

6.0 

26.2 

6.1 

24- 3 

6-3 

22.9 

6-5 

21.6 

6.1 

21 .0 

4-7 

19.7 

2. 1 

19.2 

.0 

cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 


87 
95 
92 

79 
78 
79 
85 
68 

33 
2. 


1  In  neither  series  I  or  II  were  stops  provided  for  the  exhaust  cock.    This  is  the  case  in  series  III,  et  seq. 

'Filter  open  900  without  danger.     Evaporated  corona  shows  *=»  7.6. 

•Coronas  at  first  stone-blue  and  irregular,  soon  becoming  gBP. 

*CleargB  P  at  once. 

•For  air,  «=  9.9  w  o  g.     n X  io-3=  290.     Large  coronas  fall  out,  leaving  a  smaller  one  behind. 


4o 


VAPOR    NUCLEI    AND    IONS. 


Several  interesting  features  are  seen  in  the  radium  and  X-ray  curves  in 
fig.  23,  to  which  special  attention  may  be  called.  It  will  be  observed  that 
the  curves  for  distances  D  =  io  and  20  cm.  of  the  anticathode  from  the 
sides  of  the  fog  chamber  begin  and  terminate  in  nearly  coincident  curves 
and  coronas,  but  that  they  lie  at  some  distance  apart  in  their  middle 
regions.  Hence  available*  nuclei  are  apparently  not  more  numerous 
eventually  in  one  case  than  in  the  other,  but  they  are  larger  (virtually) 
in  the  middle  regions  for  the  stronger  radiations;  in  other  words,  the 
asymptote  is  more  quickly  approached  for  the  stronger  radiation. 


300 


ZOO 


20  Z5  30  35  40 

Fig.  23. — Efficient  nucleations  (n)  in  dust-free  air,  energized  or  not,  as  specified 
at  different  exhaustions  (dp).     Table  14. 

Again,  the  terminal  corona  in  case  of  the  data  for  X-rays  is  reached  long 
after  the  final  coronas  for  the  weak  radiation  from  radium  (10  mg. 
io,oooX);  i.e.,  the  number  of  nuclei  (ions)  in  the  case  of  the  weak 
radiation  ceases  to  increase  in  a  region  of  lower  exhaustion,  apparently, 
than  the  one  observed  for  the  more  intense  radiation.  Hence  in  case  of 
the  latter,  finer  gradations  of  nuclei  appear  to  occur,  as  if  the  radiation 
shattered  certain  of  the  larger  ions.    There  is,  however,  another  point  of 

*It  will  appear  below  that  for  nuclei,  large  or  small,  the  limit  is  reached  with  the 
given  number  of  nuclei  per  cubic  centimeter,  corresponding  to  the  g  B  P  corona.  Nuclei 
in  excess  of  this,  large  or  small,  are  inefficient. 


EFFICIENCY    OF    FOG    CHAMBER.  41 

view  to  which  some  probability  may  be  assigned.  In  the  case  of  intense 
radiation  relatively  large  and  possibly  persistent  nuclei  are  produced  in 
greater  numbers,  and  these  may  capture  much  of  the  moisture  and 
prevent  condensation  on  the  smaller  ions,  until  proportionately  larger 
exhaustions  have  been  applied.  Examples  of  these  occurrences  will  be 
given  in  the  next  paragraph. 

CONNECTING  PIPES  TWO  INCHES  IN  DIAMETER. 

39.  Remarks  on  the  method. — The  connection  between  fog  cham- 
ber and  vacuum  chamber  was  now  further  enlarged  by  using  two  nipples 
6  inches  long  and  2  inches  in  diameter,  on  either  side  of  a  plug  stopcock 
of  2\  inches  bore.  The  latter  was  chosen,  since  much  of  the  resist- 
ance was  heretofore  encountered  in  this  place.  Usually  observations 
were  taken  at  long  intervals  of  time  apart,  to  allow  for  the  dissipation 
of  water  nuclei  due  to  the  evaporation  of  very  small  fog  particles. 
Moreover,  a  considerable  period  (three  days)  elapsed  before  definite 
results  could  be  recorded.  Something  of  a  nuclei -producing  character  is 
usually  present  some  time  after  assembling  the  parts  of  the  apparatus. 
The  coronas  under  otherwise  like  circumstance  gradually  increase  to  a 
maximum.  Moreover,  in  the  absence  of  all  leakage  inward  from  without, 
periodicity  of  coronal  diameter  is  often  in  evidence  in  the  successive 
exhaustions  and  especially  active  in  case  of  the  very  large  coronas.  The 
best  results  appear  after  long  waiting  before  each  observation,  whence  it 
follows  that  evaporation  from  the  heavy  paraffin  oil  used  for  tightening 
the  stopcocks,  leakage  of  nuclei  through  the  filter  or  through  unknown 
channels  is  quite  ineffective.  Waiting  was  finally  made  needless  by  first 
exhausting  the  partially  exhausted  fog  chamber  before  each  definite 
observation.  The  effective  drop  of  pressure  is  then  small  and  only  the 
large  nuclei  are  caught  and  the  fog  particles  do  not  evaporate  appreciably. 
The  filter,  moreover,  in  all  tests  gives  evidence  of  entire  trustworthiness. 
It  was  customary  to  open  and  close  the  plug  cock  quickly,  between  stops, 
a  spring  opening  device  having  been  put  in  action.  In  no  case  was  there 
danger  of  under-saturation,  the  wet  cloth  linings  being  but  8  or  10  cm. 
apart,  above  and  below.  In  the  highest  exhaustions  used,  ^  =  44  cm. 
about,  the  volume  expansion  is  fully  2.5,  so  that  60  per  cent  of  the  air 
must  thereafter  be  readmitted  freshly  through  the  filter.  Naturally  in 
this  slow  passage  it  would  be  not  only  denucleated  but  deionized,  if  there 
were  not  fresh  sources  of  penetrating  radiation  always  in  action  for  the 
reproduction  of  both  types  of  nuclei.  In  general  the  apparatus  seems  to 
have  behaved  faultlessly.  Such  irregularities  as  remain  must  then  in 
large  measure  have  been  introduced  by  the  fact  that  the  drop  of  pressure 


42 


VAPOR    NUCLEI    AND    IONS. 


was  observed  at  the  fog  chamber  when  isothermal  conditions  had  been 
reestablished.  It  should  have  been  computed  from  the  initial  pressures 
of  both  chambers  and  their  common  isothermal  pressure  when  in  com- 
munication, in  the  way  shown  in  the  next  section.  The  present  results, 
however,  suffice  for  comparison  with  the  preceding  and  following  work, 
and  it  is  probable  that  limiting  conditions  of  efficiency  have  already  been 
reached.  That  this  is  actually  the  case  will  also  be  shown  in  the  next 
section. 

40.  Data  for  pipes  2  inches  in  diameter,  12  inches  long. — The  results 
obtained  are  fully  given  in  table  15.  It  appears  that  coronas,  even  above 
the  large  green-blue-purple  type,  appeared  at  the  high  exhaustions,  but 
this  is  not  quite  certain. 

Incidentally  some  data  on  the  effect  of  X-rays  from  different  distances 
are  included  in  the  tables  (part  VI  et  seq.).  The  usual  difficulty  of  an 
inconstant  X-ray  bulb  appears.  Moreover,  certain  peculiar  results  on 
the  distribution  of  the  nuclei  within  the  fog  chamber  in  case  of  symmet- 
rical exposure  to  weak  radium  are  here  again  noticed  (part  V),  as  in 
Chapter  I,  section  4.  The  results  are  plotted  in  fig.  24  and  smooth 
curves  obtained  therefrom  are  shown  in  fig.  25. 

Table  15. — Air  nucleation  at  different  supersaturations.  Piping  2  inches  in  diameter, 
12  inches  long;  plug  gas  cock,  2$  inches  in  bore.  Wait  30  minutes  between  observa- 
tions. Angular  diameter  of  coronas,  2  sin-1  s/60.  Eye  40  cm.,  lamp  250  cm.,  on 
opposite  sides  of  fog  chamber,     dp  observed  isothermally  at  the  fog  chamber. 


Coro- 
na. 


nx 


I.  Non-energized  dust- 
free  air. 


35.4 

14 

gBP 

35-3 

14 

gBP 

40.6 

«4 

gBP 

44.4 

14 

'gBP 

41.4 

14 

gBP 

36.6 

14 

gBP 

33-0 

14 

gBP 

3*1 

gyo 

29-5 

10.3 

wr'g 

27.7 

6.4 

wr'g 

29-3 

10.4 

wr  g 

28.0 

^6.7 

wrg 

26.  2 

%2.6 

Fcor 
fear 

26.0 

.'3-i 

24.0 

Ti   O 

£cor 

27.2 

hi 

wy'g 

480 
480 
510 
540 
520 
490 
470 

410 

250 

91 
250 
104 

6. 
9- 

120 


Coro- 
na. 


nx 


Non-energized  dust- 
free  air — Cont'd. 


28.0 

7-7 

wPcor 

28.9 

10.6 

wrog 

30.8 

12.5 

gyo 

31.8 

12.8 

gyo 

330 

130 

gBP 

170 
280 
410 
420 

470 


II.  Air  energized  by  X- 
rays;  D=  10  cm. 


33-3 
35-0 
39-8 

3i-7 
26.9 

24-5 
23-3 
21 .0 


(2) 

(*) 

(3) 

13-5 

b'BP 

b'BP 

b'BP 

n-5 

b'BP 

11. 7 

gBP 

13 

wo  bg 

470 
480 
510 

460 
420 

390 
380 
230 


Coro- 
na. 


nx 


II.  Air  energized  by  X-rays; 
D  =  10  cm. — Cont'd. 


20.4 

9.0 

wcg 

21  .O 

11. 4 

w  obg 

19.7 

6.2 

wr  bg 

19. I 

4.1 

cor 

18.4 

i-3 

cor 

I7.4 

.0 

170 

230 

190 

19 

I 
o 


Continued,  next  day; 
D=*  10  cm. 


18 
18 
18, 
20. 
20. 
21 . 


5 

4o 

5 

0 

9 

1.6 

cor 

3 

6.8 

wrg 

9 

9-3 

wcg' 

9 

gyo 

o 
o 

2 

87 
l80 
330 


1  Stone- blue  colors,  above  gBP. 

2  Irregular.     Shows  strong  purple   band  just 

above  water.     Coronas  diffuse. 


8  Stone- blue. 

♦Left   over  night  seems  to  diminish  rainlike 
condensation. 


EFFICIENCY    OF    FOG    CHAMBER. 
Tabi^e  15.  — Continued. 


43 


dp. 


Coro- 
na. 


nX 


III.  Air  energized  by  X- 
rays;  D=6o  cm. 


175 
19. 1 
20.3 
21 .0 
22.5 
22.8 

23  -5 
24.8 
26.6 
26.6 
30.9 
35-8 


0.0 

1.7 

6.1 

8.7 
11. 7 
12.2 
li3.o 


cor 
wr  g 
wc  g 

wog' 
wog' 

gyo 
gyo 
gyo 
gyo 
gyo 
gyo 


2 

65 
180 
250 
270 
340 
350 
370 
370 
410 
440 


IV.  Air  energized  by  X- 
rays;    D=*6oo. 


40.0 

8.7 

36.0 

7-3 

cor 

3i-7 

6.1 

cor 

27.2 

5-2 

cor 

24.4 

5-2 

cor 

23.0 

5-2 

cor 

21.0 

50 

cor 

19.4 

.0 

19.4 

.0 

18. 1 

.0 

20.3 

3-i 

cor 

21 .0 

4.8 

cor 

23.0 

5-7 

cor 

26.3 

5-4 

cor 

310 

5-8 

cor 

35-3 

26.9 

cor 

35-4 

6.8 

cor 

39-8 

8.1 

w  r 

44-3 

10. 0 

w  0 

44-4 

SIO.O 

w  0 

250 

150 

90 

52 

50 

46 

39 
o 
o 
o 

8 

35 

60 

57 

76 

130 

125 

205 

322 

322 


44-3 
40.2 

35-9 
33-5 
30.8 
27.0 
24.4 
23.2 
20.9 
20.5 
19.4 
18.3 


dp. 


Coro- 
na. 


nX 
io-s 


V.  Air  energized  by  radi- 
um (10  mg.  10,000 X); 
Z?  =  o,  on  side. 


49-7 

w  o' 

7-5 

w  r* 

6.6 

w  0 

6.6 

w  r 

6.5 

w  r 

6.1 

w  r 

5-8 

w  r 

6.2 

cor 

5-8 

cor 

4-7 

cor 

1.3 

cor 

.0 

305 
153 

"5 
in 
103 
79 
436 

74 
60 
32 

1-3 

.0 


VI.  Air  energized  by  X- 
rays. 


'22.9 
'22.9 
22.9 
'22.9 


5-5 
7-3 
7-7 
97 


wr  g 
wyg 
wlBP 
wcg 


no 
140 
200 


VII.  Air  energized  by  X- 
rays;  D=  200  cm. 


19.0 

2. 1 

cor 

20.3 

6.8 

wr  g 

20.9 

7-4 

wg 

22.8 

7.5 

!gBP 

25-9 

7-5 

gBP 

3i-i 

u7'4 

wyg 

304 

"7-4 

wog 

35-5 

u7'4 

wog 

35-i 

"7-4 

wog 

40.0 

74 

wog 

43-9 

7.0 

wrog 

2 

85 
105 
125 
135 
135 
130 

135 
135 
145 
135 


9P. 


Coro- 
na. 


n  x 


VIII.  Air  energized  by  X- 
rays;  Z?=6oo  cm.;  re- 
peated for  contrast. 


43-9 
46.8 
48.8 

10.7 
10.6 
10.5 

wog 
wog 
wog 

300 
310 
320 

IX.  Air  energized  by  X- 
rays;  D=  100  cm. 

44.4 

7 

6 

w|BP 

41.9 

7 

6 

w|BP 

36.2 

7 

6 

gBP 

31.8 

7 

6 

gBP 

25 -4 

lOg 

8 

wcg7 

26.5 

9 

2 

wrg 

24.0 

9 

3 

wcg 

21.6 

8 

2 

w|BP 

20.8 

7 

4 

wyg 

20.3 

5 

5 

cor 

19.7 

u4 

1 

cor 

28.0 

8 

8 

wcg' 

316 

7 

8 

g|BP 

180 
170 
160 
150 

200 
205 

195 
130 
105 
50 
19 
215 
170 


X.  Air  energized  by  X-rays; 
D=  50  cm.  from  end. 


30.8 

8.8 

wrg 

35.6 

8.7 

wPcor 

40.1 

8.2 

wPcor 

230 

220 
205 


XI.  The  same;  #=50  cm. 
Bulb  more  efficient. 


31.6 

9-8 

wcg 

27.0 

IO.8 

wrog 

25.2 

IO.9 

wrog 

22.  2 

IO. O 

wcg 

20.3 

6.1 

wrg 

35-1 

9.2 

wcg 

4O.O 

8.3 

wPcor 

44.O 

7-8 

w|BP 

48.7 

7-7 

g,BP 

32.2 

10.4 

wrog 

245 
235 
225 
200 

65 

240 
205 
180 
190 

260 


1  As  intensity  of  ionization  increases  there  is 

less  shattering. 

2  Next  day.     Fog   chamber    absolutely   tight. 

Coronas  all  blurred. 

3  The  final  use  in  response  to  new  conditions. 

4  Coronas  blurred  and  larger  at  the  glass  end  of 

fog  chamber. 
•D  =  6oo  cm. 


®D  =  3,000  cm. 
7D=  150  cm. 
*D=  75  cm. 

9  Long  waiting   (£  hour  to  2  hours)   without 

effect. 

10  Passing,  as  usual,  through  a  maximum. 

11  Fog  limit  below  20. 


44 


VAPOR    NUCLEI    AND    IONS. 


41 .  The  same,  continued.  X=ray  bulb  inclosed  in  lead . — In  the  experi- 
ments detailed  the  X-ray  bulb  was  not  inclosed,  so  that  secondary 
radiation  issued  from  the  whole  surrounding  environment.  In  the  data 
given  in  table  17  the  bulb  is  surrounded  by  a  wide  lead  box,  containing  a 
window  7.5  cm.  in  diameter  fronting  the  fog  chamber.  The  window 
was  in  a  removable  side  or  lid  of  the  box.  This  was  kept  at  a  long 
distance  (D  =  6oo  cm.)  in  order  to  furnish  weaker  ionization  than  was 
specified  in  table  15. 

h' 

9 

500 


400 


300 


200 


100 


20  25  30  35  40 

Fig.  24. — Efficient  nucleations  in  dust-free  air,  energized  or  not  by  radium  or  the  X-rays 
from  different  distances  (D)  and  different  exhaustions  (dp).  X-ray  bulb  not  within 
lead  case,  unless  stated. 


In  the  first  part  of  table  16  the  exhaustion,  dp  =  27  cm.,  lies  below  the 
fog  limit  of  dust-free  air.  The  low  degree  of  ionization  is  thus  shown 
under  different  conditions.  The  second  series  contains  a  number  of 
successive  exhaustions  for  an  increasing  dp,  with  the  radiation  passing 
through  a  thin  tin  plate.     Parts  III   and   IV  of  the  table  are  similar 


DISTRIBUTIONS    OF    NUCLEI. 


45 


series,  with  the  window  open  (tin  plate  removed),  the  last  series  being 
a  detail  for  the  initial  part  of  the  curve,  which  is  of  especial  interest. 
The  results  are  also  shown  in  fig.  24,  where  their  relation  to  the  lowest 
curve,  D  =  6oo  cm.,  for  the  open  or  non-inclosed  X-ray  bulb  becomes 
evident.  In  each  of  these  curves  there  is  a  definite  horizontal  branch 
within  which  the  ions  predominate.  Beyond  this  lies  the  rise  due  to  the 
colloidal  nuclei,  but  the  curves,  and  particularly  the  asymptotes,  are 
depressed  in  both  cases. 


Table  16. — Nucleations  at  different  exhaustions.  2^-inch  cock,  2-inch  piping,  12 
inches  long.  X-ray  bulb  in  lead  case  at  D  =  6oo  cm.  from  glass  fog  chamber. 
Aperture  in  case  7.5  cm.  in  diameter. 


Lead  box. 

s. 

Cor. 

1 
dp. 

n  Xio~3. 

I.   Window  open 

3-i 
.0 

cor 
cor 

20.5 
20.5 

8-4 
.0 

Window  closed  with  lead. 

Window  open 

3-4 
2.9 

cor 

20.5 
20.5 

11. 7 
6.8 

Window  closed  with  tin1. 

cor 

Front  lead  side  off2 

3-5 

cor 

20.5 

13.0 

II.  Closed  with  tin  plate.  .  . 

.0 

cor 

18.6 

.0 

30 

cor 

20.6 

7-6 

2.7 

cor 

22.3 

6.4 

2.8 

cor 

23-7 

7.0 

4.1 

cor 

26.8 

24-3 

12.0 

wybg 

31.2 

380 

gBP 

34-7 

480 

III.  Tin  plate  off 

3wy  b  g 
wog 

33-8 
310 

400 
305 

5-2 

w  r 

28.0 

55 

4.2 

cor 

26.6 

26 

4.1 

cor 

24- 5 

23 

4.2 

cor 

22.5 

24 

3-4 

cor 

20.7 

12 

2.6 

cor 

20.0 

5-2 

Tin  plate  on 

i-7 

2-5 

3-8 

cor 

20.0 

i-7 

4.8 

17 

IV.  Tin  plate  off 

cor 

20.0 

cor 

21.5 

4.2 

cor 

22.0 

24 

4.0 

cor 

22.7 

20 

4.0 

cor 

24.0 

21 

1  Open  side  over  i  foot  square. 

2 Lead  sheet  o.  12  cm.  thick;  tin  plate  0.03  cm.  thick. 


3  After  long  waiting. 


42.  Discussion. — It  will  now  be  in  place  to  make  a  more  complete 
survey  of  the  manifestations  of  nucleation  in  dust-free  air  under  any 
conditions.  Figs.  24  and  25  are  useful  for  this  purpose.  With  regard 
to  the  method  I  may  recall  that  the  difficulties  were  enhanced  by  the 
need  of  providing  rapid  exhaustions  in  case  of  a  fog  chamber  large 
enough  to  measure  the  coronas  and  to  show  the  sequence  of  axial  colors. 


46 


VAPOR    NUCLEI    AND    IONS. 


The  earliest  results  (Chapter  I,  section  12)  scarcely  captured  the  maximum 
of  30,000  nuclei  under  the  extreme  exhaustion  corresponding  to  the 
limiting  asymptote  (marked  "preliminary"  in  fig.  24).  In  proportion 
as  the  apparatus  was  perfected,  this  asymptote  was  raised,  step  by  step, 
until  nucleations  of  at  least  500,000  were  leftinthe  exhausted  fog  chamber. 
Probably  the  asymptote,  or  more  accurately  the  terminal  corona,  obtained 
in  any  given  type  of  apparatus,  indicates  that  the  limit  of  condensing 


30      c      35 

DECR.  SIZE—** 

Fig.  25 — Smooth'curve  from  fig.  24.  Nucleation  (AT)  of  dust-free  air,  in  thousands  of 
nuclei  per  cubic  centimeter,  energized  or  not,  as  stated,  by  weak  radium,  or  by  the  X-rays, 
at  different  distances  {D  in  cm.).  The  letters  attached  to  the  curves  indicate  the 
characteristic  colors  of  the  inner  field  (or  its  margin)  of  the  largest  coronas,  the  order 
of  colors  being  R,  O,  Y,  G,  B.  The  abscissas  show  the  observed  isothermal  drop  of 
pressure  by  which  the  supersaturation  is  produced  and  the  nucleations  applied  rela- 
tively to  the  given  apparatus.  The  line  marked  "air"  shows  the  behavior  of  dust-free 
non-energized  air  terminating  in  the  large  green  coronas.  In  a  perfect  apparatus 
supersaturation  would  increase  enormously  beyond  a;  the  droplets  would  be  at  freez- 
ing beyond  b.  In  the  given  apparatus  efficiency  probably  ceases  beyond  c  when  damp 
air  is  the  medium. 


power  has  been  reached.  Between  the  fog  limit  and  the  terminal  corona 
the  graph  rises  in  a  straight  upward  sweep;  and  it  is  remarkable  that 
the  rates  at  which  the  nucleation  decrease  with  the  drop  of  pressure,  or 
better  with  the  volume  expansion,  are  about  the  same  between  fog  limit 
and  asymptote,  no  matter  whether  they  lie  within  the  region  of  high 
supersaturation  characteristic  of  the  colloidal  nuclei  or  in  the  region 
of  relatively  low  supersaturation  characteristic  of  ionized  air.    Moreover, 


DISTRIBUTIONS    OF    NUCLEI.  47 

they  are  the  same  in  any  apparatus,  within  the  limits  of  its  efficiency. 
In  fact,  even  the  curve  which  I  have  endeavored  to  reduce  to  the  same 
scale  from  Wilson's  disk  colors  for  non-energized  dust-free  air  (apart 
from  differences  in  the  meaning  of  dp  to  be  explained  in  the  next  sec- 
tion) lies  in  the  same  region  of  pressure  difference,  and  shows  a  slope 
quite  in  keeping  with  the  other  curves.*  For  an  imperfect  apparatus, 
on  the  other  hand,  the  slope  terminates  abruptly  at  a  lower  asymptote 
and  in  a  region  of  higher  exhaustion.  It  will  be  convenient  to  refer 
to  the  nuclei  belonging  to  the  slopes  specified  as  representative  nuclei. 

To  obtain  the  curve  for  the  colloidal  nuclei  of  dust-free  air,  it  is  often 
necessary  to  wait  a  week  or  more,  until  unknown  internal  sources  of 
nucleation  have  spent  themselves.  Moreover,  the  isolated  observations 
made  with  advantage  ought  to  be  made  hours  apart,  for  it  is  with  the 
exhaustion  that  the  release  of  spurious  internal  nuclei  occurs,  suggesting 
that  water  nuclei  due  to  the  evaporation  of  small  fog  particles  are  possibly 
in  question. 

The  air  curve  passes  through  the  first  two  cycles  of  large  coronas, 
terminating  beyond  the  highest  green-blue-purple,  actually  in  the 
stone-blue  or  higher  coronas,  the  first  of  the  series  producible  in  the 
fog  chamber  by  any  means  whatever.  It  corresponds  with  the  opaque 
of  the  steam  jet,  beyond  which,  however,  there  exists  another  cycle 
of  yellows,  to  my  knowledge  beyond  the  reach  of  the  fog  chamber.  It 
is  not  probable  that  the  medium  is  as  yet  quite  optically  inactive  after 
the  bluish  coronas  specified,  but  merely  appears  so  in  small  thicknesses. 

If  we  turn  from  the  curve  of  non-energized  air  to  the  case  of  weak 
ionization  such  as  is  produced  by  10  mg.  of  impure  radium  (i 0,000  X) 
or  by  the  X-rays  from  a  distance  of  6  meters,  we  may  note  in  the  first 
place  that  the  coronal  fog  limit  has  enormously  decreased  as  compared 
with  its  position  in  dust-free  non-energized  air.  The  nuclei  are  therefore 
throughout  correspondingly  larger  in  size.  The  nucleation  soon  rises 
with  an  approach  to  the  characteristic  slope  referred  to,  showing  that 
the  representative  ions  lie  within  a  relatively  narrow  range  of  sizes,  the 
curve  of  distribution  terminating  in  a  maximum.  With  increasing 
exhaustion  the  nucleation  first  decreases  to  a  minimum;  hence  to  all 
appearances  the  ions  are  now  partially  destroyed  or  else  materially 
reduced  in  size  at  low  pressure,  so  as  to  fail  of  capture  even  in  the  higher 
exhaustions.  Beyond  the  minimum  the  final  and  most  interesting  stage 
of  variation  characteristic  of  weak  ionization  may  be  observed.  The 
nucleation  rapidly  rises  again,  eventually  to  approach  the  asymptote  of 
dust-free  air.     In  explanation  of  this  phenomenon,  we  may  agree  that 

♦The  coincidence  between  my  interpretation  of  Wilson's  disk  colors  and  my  own  data 
holds  only  when  the  drop  of  pressure  is  observed  at  the  fog  chamber.     »See  section  48. 


48  VAPOR    NUCLEI    AND    IONS. 

further  nuclei  are  destroyed  or  rendered  relatively  inefficient  by  the 
low  pressure  until  there  is  a  sufficient  excess  of  supersaturation  to  actually 
capture  the  colloidal  nuclei  of  dust-free  air  more  and  more  fully  in  the 
presence  of  the  ions  (few  in  number  and  small  in  size)  remaining.  Pos- 
sibly the  relative  number  of  ions  and  colloidal  nuclei  is  itself  a  suffi- 
cient reason;  but  it  since  seems  clear  that  an  apparatus  which  ceases 
to  produce  condensation  on  colloidal  nuclei  much  below  dp  =  35  cm. 
can  not  be  expected  to  regain  efficiency  between  ^  =  35  and  dp  =  45 
cm.,  unless  there  is  destruction  of  whatever  has  been  holding  down  the 
effective  nucleation  to  low  numbers.  As  the  ions  decrease  either  in  size 
or  number,  there  is  a  reappearance  of  the  normal  colloidal  nucleation 
of  dust-free  air.     Its  asymptote  is  less  and  less  depressed. 

Under  moderate  ionization,  such  as  is  obtained  from  the  X-ray  bulb 
at  a  distance  of  1  to  2  meters,  the  fog  limit  is  definitely  reduced,  showing 
the  presence  of  an  order  of  larger  nuclei;  the  asymptotes  are  correspond- 
ingly higher  and  they  are  reached  later  (i.  e.,  at  higher  exhaustions), 
indicating  the  presence  of  smaller  nuclei  than  in  the  preceding  cases, 
as  well  as  larger  nuclei,  unless  the  increased  presence  of  the  latter  retards 
condensation  on  the  former.  The  range  of  sizes  within  which  the  repre- 
sentative nucleations  lie  is  definitely  extended  in  both  directions,  but 
particularly  on  the  sides  of  the  smaller  nuclei.  The  maximum  and  the 
minimum  are  flattened,  though  destruction  of  ions  still  occurs  at  low 
pressure. 

The  new  feature  of  these  curves  is  their  failure  to  rise  from  the  mini- 
mum toward  the  asymptote  of  dust-free  air.  It  follows  that  the  ions 
are  now  present  in  too  large  a  number,  even  relatively  to  their  reduced 
sizes  at  high  exhaustion  (if  this  obtains),  to  leave  an  excess  of  super- 
saturation  sufficient  to  catch  the  colloidal  air  nuclei;  or,  from  the  other 
point  of  view,  the  kinetic  ionization  pressure  is  too  strong  to  admit  of 
sufficient  rupture  of  the  nuclei  even  at  the  lowest  pressures  applied. 
(Section  43.) 

In  the  comparison  of  both  series  of  experiments,  the  occurrence  of 
the  intersection  of  the  curve  is  noteworthy.  In  other  words,  the  nuclea- 
tion, apparently  produced  at  high  exhaustion  by  an  X-ray  bulb  at  6 
meters  from  the  fog  chamber,  may  be  much  larger  than  the  nucleation 
produced  from  200,  100,  or  even  50  cm.,  due  (as  we  have  supposed)  to 
the  reappearing  efficiency  of  the  colloidal  nuclei  in  the  former  case. 
Similar  complications  surround  the  distance  effects  at  other  pressures; 
but  under  conditions  of  sufficiently  moderate  exhaustion,  i.  e.,  below 
the  fog  limit  of  filtered  air,  the  distance  effects  between  50  and  600  cm. 
remains  disproportionately  small. 

When  the  ionization  is  relatively  intense,  as  when  the  anticathode  is 
from  10  to  60  cm.  from  the  thinner  side  of  the  glass  fog  chamber,  the 


DISTRIBUTIONS    OF    NUCLEI.  49 

fog  limit  has  decreased  somewhat  further,  showing  increased  abundance 
of  the  larger  nuclei;  but  the  slope  closely  resembles  the  corresponding 
case  for  dust-free  air.  There  is  no  maximum,  but  a  terminal  asymptote, 
or  better,  a  terminal  corona  of  fixed  aperture.  This  corona,  which  is 
here  the  largest  obtainable  in  the  fog  chamber,  is  even  at  the  highest 
ionizations  reached  at  supersaturations  below  the  coronal  fog  limits 
for  dust-free  air,  and  long  before  the  apparatus  has  ceased  to  function. 
It  is  impossible  to  state  whether  colloidal  nuclei  are  simultaneously 
present  but  inactive  or  whether  their  inefficiency  is  due  to  actual  absence. 
It  thus  becomes  a  problem  of  great  theoretical  importance  in  its  bearing 
on  this  subject  to  determine  how  the  precipitated  super  saturation  is 
distributed  among  groups  of  nuclei  of  different  sizes. 

It  is  finally  to  be  observed  that  the  terminal  corona  is  the  same,  both 
for  the  ionized  and  the  non-ionized  state  of  the  gas.  The  maximum 
number  of  nuclei  which  can  be  caught  per  cubic  centimeter  seems,  there- 
fore, to  be  a  constant  for  the  apparatus  and  the  medium  inclosed,  and 
to  be  independent  of  the  size  of  the  nuclei,  whether  large  like  the  ions 
or  small  like  the  colloidal  nuclei.  In  the  above  apparatus,  with  an  air- 
water  medium  it  is  difficult  to  pass  beyond  the  large  green-blue-purple 
corona. 

43.  Radiant  fields. — The  occurrence  of  a  succession  of  groups  of 
colloidal  nuclei  of  (let  us  say  for  simplicity)  continuously  decreasing  size 
and  continuously  increasing  number,  is  suggestive;  for  each  group  is 
essential  in  the  given  natural  but  otherwise  unknown  environment. 
They  are  at  once  restored  if  withdrawn.  These  conditions  may  be  imi- 
tated or  varied  artificially  by  approaching  the  radium  tube  at  different 
distances  from  the  fog  chamber,  in  which  case  the  efficient  nucleation 
will  for  weak  radiation  usually  decrease,  as  the  intervening  distances 
are  smaller. 

Furthermore,  in  the  presence  of  radium  the  character  of  the  phenom- 
enon is  the  same,  except  that  the  nuclei  are  throughout  larger.  With- 
drawn by  precipitation  they  are  at  once  restored.  They  are  an  essential 
part  of  air  in  the  new  (radiant)  environment  and  the  nuclei  are  again 
graded. 

It  is  natural  to  compare  the  particular  nuclear  status  introduced  in  the 
latter  case  by  a  particular  kind  of  radiation  (gamma-rays)  with  a  former 
case  of  dust-free  air  in  the  absence  of  recognized  radiation.  In  other 
words,  if  we  abstract  from  the  details  of  the  mechanism  which  are  un- 
known for  the  colloidal  nuclei,  chemical  agglomeration  might  be  con- 
sidered referable  to  some  radiant  field,  unknown  but  otherwise  essentially 
alike  in  kind,  to  the  much  coarser  nucleations  observed  on  exposure  to  the 
known  radiant  field.    The  effect  of  radium,  however  distant,  is  virtually 


50  VAPOR    NUCLEI    AND    IONS. 

an  increase  of  size  of  the  efficient  air  nuclei  and  a  decrease  of  their  number. 
Hence  if  we  were  to  fancy  that  the  colloidal  nucleation  of  air  responds 
to  its  own  radiant  environment,  this  would  have  to  be  special  in  kind. 

Recently  I  have  made  similar  tentative  inquiries  as  to  whether  the 
ions  and  persistent  nuclei  might  not  be  regarded  as  colloidal  nuclei 
aggregated  by  kinetic  pressure,  corpuscular  or  undulatory;  for  in  view 
of  the  occurrence  of  pronounced  secondary  action  within  the  fog  chamber, 
the  radiation  at  any  point  must  be  considered  as  sufficiently  the  same  in 
all  directions  to  be  equivalent  to  a  Lesage  medium.  It  is  then  possible 
to  account  for  the  nucleation  in  any  ionized  field,  for  fleeting  and  per- 
sistent nuclei,  for  condensational  differences  of  positive  and  negative 
ions,  for  fleeting  nuclei  otherwise  identical  but  respectively  charged  and 
uncharged,  for  the  destructive  effect  of  low  pressure  and  the  counter- 
action in  strong  ionized  fields,  for  electrical  differences  in  the  effect  of 
ultra-violet  light  and  of  X-rays,  etc.,  with  a  single  straightforward 
hypothesis. 

While  such  a  view  may  be  worth  a  statement,  it  would  at  the  outset 
encounter  very  determined  opposition;  and  the  distinctive  or  differen- 
tiating evidence  to  sustain  it  is  uncertain.  Briefly,  if  we  admit  that 
with  ions  sufficiently  large  and  sufficiently  numerous,  relatively  speaking, 
the  colloidal  nuclei  are  virtually  non-existent  (so  far  as  the  fog  chamber 
is  concerned),  since  the  former  capture  all  the  available  moisture,  most 
of  the  phenomena  of  nucleation  admit  of  interpretation,  and  additional 
hypotheses,  however  alluring,  are  not  called  for.  Moreover,  so  long  as 
the  representative  colloidal  nuclei  are  definitely  smaller  than  the  smaller 
ions,  even  in  the  strongest  electrical  field — in  other  words,  if  what  may 
be  called  the  shattering  action  of  strong  fields  always  fails  to  reveal 
ionized  nuclei  as  small  as  the  representative  colloidal  nuclei — the  special 
interpretation  is  not  warranted. 

In  conclusion,  if  we  asked  what  is  the  most  important  outcome  of 
researches  of  the  present  character,  I  should  refer  to  the  appearances 
obtained,  indicating  that  a  gas,  or  at  least  a  moist  gas,  far  from  being  a 
uniform  system,  behaves  like  an  assemblage  of  nuclei  which  decrease  in 
size  and  increase  in  number  as  the  molecular  dimension  is  approached. 
Every  group  of  nuclei  is  none  the  less  a  structurally  essential  part  of  the 
gas  and  (be  the  number  of  groups  few  or  many)  is  at  once  restored  if 
withdrawn,  while  the  molecule  itself  is  distinguished  among  the  many 
nuclei  of  its  own  kind  by  the  maximum  frequency  of  occurrence. 

In  the  above  cases  (fig.  25)  the  occurrence  of  nearly  identical  slopes 
for  colloidal  nuclei  and  for  strong  ionization  may  thus  be  regarded  as 
the  initial  branch  of  a  law  of  distribution  of  sizes  given  by  the  theory 
of  dissociation. 


EFFICIENCY    OF    FOG    CHAMBER.  51 

COLLOIDAL    NUCLEI   IN  DUST-FREE   AIR.     EXHAUSTION    PIPES  AND 
STOPCOCKS  FOUR  INCHES  IN  DIAMETER. 

44.  Purpose. — In  the  above  experiments,  the  efficiency  of  the  fog 
chamber  in  regard  to  the  capture  of  very  small  nuclei  was  successively 
increased  by  enlarging  the  efflux  pipe  in  diameter  as  far  as  2  inches. 
In  the  present  experiments  a  further  step  is  taken  by  increasing  the 
diameter  to  4  inches.  This  final  step,  however,  did  not  show  the  marked 
improvement  which  might  have  been  anticipated,  while  the  difficulty 
of  manipulating  a  plug  weighing  25  pounds  is  obvious.  The  limiting 
coronas  here,  as  above,  were  the  large  green-blue-purple  type,  and  in  no 
apparatus  of  the  present  kind  has  it  been  certainly  possible  to  exceed 
this  in  angular  aperture.  The  use  of  so  large  a  stopcock  introduces 
other  difficulties.  It  is  in  the  first  place  nearly  impossible  to  make  it 
quite  tight.  Provision  against  the  influx  of  external  air  may  be  made 
in  perfection,  by  aid  of  an  annular  oil  bath  of  the  above  form;  but  slow 
leakage  from  the  fog  chamber  to  the  vacuum  chamber  around  the  plug 
could  not  be  avoided.  This  is  an  inconvenience,  though  it  need  not 
introduce  serious  error.  With  a  tightly  packed  filter  the  air  within  the 
fog  chamber  is  never  quite  at  atmospheric  pressure,  but  a  few  milli- 
meters below  it,  so  that  the  exhaustion  begins  at  a  lower  pressure  than 
76  cm. 

45.  Apparatus. — This  is  shown  in  fig.  26,  where  F  is  the  fog  chamber, 
V  the  vacuum  chamber,  C  the  4-inch  stopcock  between,  P  the  air 
pump.  The  pressure  within  the  vacuum  chamber  is  given  by  the  gage 
G,  which  also  communicates  with  the  air  pump.  The  latter  may  be 
shut  off  by  the  glass  two-way  stopcock  c,  which  serves  also  for  the 
admission  of  dust-free  atmospheric  air  when  pressure  is  to  be  lowered 
through  the  filter  /.  The  gage  g  is  in  communication  with  the  fog  chamber 
by  the  rubber  pipe  ab,  which  contains  a  lateral  branch  (not  shown) 
with  a  fine  screw  stopcock  through  which  thoroughly  dust-free  air  may 
be  admitted  into  the  fog  chamber  from  a  long  well-packed  filter  (not 
shown)  beyond  the  cock. 

The  heavy  plug  of  the  stopcock  is  handled  at  h  and  counterpoised 
by  the  spring  p  on  a  pulley.  By  properly  adjusting  the  tension  (taking 
care  to  allow  for  excess  and  diminution  of  air-pressure),  the  plug  may 
be  rotated  as  easily  and  quickly  as  a  much  smaller  valve.  There  is  no 
evidence  that  increased  speed  in  the  rotation  of  the  stopcock  would 
have  increased  the  efficiency  of  the  fog  chamber.  The  limit  reached 
depends  rather  on  the  law  of  flow,  the  gradient  of  which  eventually 
vanishes.  The  projecting  rims,  m  and  n,  of  the  stopcock  and  lower  end 
of  the  plug,  form  annular  troughs  into  which  oil  or  mercury  may  be 


52 


VAPOR    NUCLEI    AND    IONS. 


poured  (iron  stopcock)  and  the  inflow  of  the  external  air  absolutely 
avoided.  The  cock,  moreover,  is  in  this  way  virtually  floated  in  oil; 
though  no  such  provision  is  possible  to  avoid  leakage  from  F  to  V 
through  C  as  already  stated. 

The  goniometer  for  the  measurement  of  the  angular  diameter  of  the 
coronas  is  shown  somewhat  indistinctly  at  D.  The  small  vertical  plate 
which  serves  as  the  eye  rest  is  40  cm.  from  the  axis  of  the  fog  chamber, 
to  which  it  is  rigidly  attached,  but  with  freedom  of  rotation  about  a 
vertical  and  horizontal  axis  and  translation  along  the  latter.  The  arms 
are  30  cm.  long,  opened  and  closed  by  a  tangent  screw.  The  point 
source  of  light  (not  shown,  part  of  a  Welsbach  mantle)  lies  250  cm. 
behind  the  fog  chamber,  in  the  same  horizontal  plane. 


Fig.  26. — Disposition  of  apparatus  in  case  of  fog  chamber  (F)  and  vacuum  chamber 
(V)  connected  by  a  4-inch  exhaustion  pipe,  etc. 


The  X-ray  bulb,  adjustably  placed  with  the  induction  coil  and  inter- 
rupter on  a  table  provided  with  wheels,  could  be  moved  as  near  to  the 
fog  chamber,  or  remote  from  it,  as  desirable,  with  facility. 

The  fog  chamber  itself  was  a  cylindrical  jar  of  glass,  provided  with  a 
metallic  face  held  in  place  by  bolts  and  tightened  by  a  rubber  gasket. 
Wax-resin  cement  was  used  in  liberal  quantity  everywhere,  and  internal 
metallic  parts  were  so  far  as  possible  covered  with  a  coat  of  it.  In  later 
experiments  a  cylinder  of  wet  cloth  was  placed  in  the  tube  between  C 
and  F,  to  saturate  air,  in  addition  to  the  rectangular  framework  within 
the  fog  chamber. 


EQUATIONS    OF    FOG    CHAMBER.  53 

46.  Exhaustion  difficulties. — As  the  stopcock  was  not  tight  internally, 
the  final  or  isothermal  pressure  in  the  fog  chamber  could  not  be  regis- 
tered. In  any  case  it  is  doubtful  whether  the  cock  can  be  closed  again 
quickly  enough.  It  was  therefore  customary  in  the  following  experi- 
ments to  put  the  vacuum  chamber  and  the  fog  chamber  in  contact  for 
a  short  time,  after  isothermal  conditions  had  been  reestablished.  Long 
communication  between  the  fog  chamber  and  the  vacuum  chamber  is 
unadvisable  from  other  points  of  view,  since  the  character  of  the  nuclea- 
tion  of  the  latter  is  not  so  well  guaranteed  It  is  therefore  necessary 
to  ascertain  the  conditions  under  which  exhaustion  takes  place. 

Let  v  be  the  volume  of  the  fog  chamber,  V  the  volume  of  the  vacuum 
chamber,  k/c  the  ratio  of  specific  heats  of  the  moist  gas,  and  let  p,  v,  t,  p, 
denote  its  pressure,  volume,  absolute  temperature,  and  density,  under 
conditions  given  by  the  subscripts.  It  will  be  convenient  to  refer 
to  the  vacuum  chamber  by  the  same  symbols  with  accents.  Hence  the 
successive  thermal  states  will  be  for  dry  air, 


For  the  fog  chamber . 


For  the  vacuum  chamber . 


Initially ^=76,  »  p 

Adiabatically  (alone) px  r,  p, 

Isothermally(alone) p2  t2  =  t  p.,=  pt 

Isothermally  (together) .  .  .    p3  r:i  =  r  p3 

Initially p'  t'  =  t  p' 

Adiabatically  (alone) ....    p' ',  =-  pi  t'x  p\ 

Isothermally  (alone)  .  .  .  .    p'2  t'2  =  t  p'2  =  p' 

Isothermally  (together) .  .    p'3  =  p3  r'3  =  r,  p'3  =  p:i 


The  equations  describing  the  transformations  are  (again  for  dry  air) 

(k-c)/k 


[p    =Rpr  p'    =Rp'r 

I   p^Rp^  p'x  =Rp\t 

p2  =  Rp2r  =  RPit  p'i  =  Rp'2r  =  Rp\r 

p3  =  Rp3r  orp2  /p'2  =  P2/p'2 

3.  ■  •  .Pv  +  P1V=P1v  +  p'\V  =  P2v  +  Pr2V=P3  (v+V) 

From  these  one  may  deduce,  relative  to  the  value  of  pv 
v  (p(k-c)/kpiC/k-  p3)  =  V  (p3  -  p'(k-c)/kpc/k} 
or 

C/k-  ^(l+W^) 

4 Pl°  p'(k-c)/k+  (v/ v)  p  {k-c)/k 

5 p'%  +  p2'V/V  =  pt(i+v/V) 


54 


VAPOR    NUCLEI    AND    IONS. 


where  p,  p',  p3,  are  observable  with  certainty.  While  equation  (5)  is 
variously  useful  in  checking  the  results,  it  does  not  admit  of  the  indi- 
vidual determination  of  p2  and  p'2.  For  this  purpose,  however,  the 
equations  (1)  and  the  second  and  third  of  group  (2)  are  available,  with 
the  results  (for  dry  air) 


6 p2=p(k-c)/kptc/k 


p'2=p'(k-c)/kpic/k 


since  pxc/k  is  given  in  equation  (4). 

Using  these  equations,  the  data  of  table  17  were  computed,  in  con- 
nection with  incidental  results  tested  for  the  purpose. 

Table  17. — Values  of  adiabatic  (/>,)  and  isothermal  (p2,  p'2)  pressure  for  dry  air.  Pres- 
sures computed  from  the  initial  pressures  (/>  =  76,  p')  and  the  final  common  isothermal 
pressure  p3  of  the  communicating  fog  and  vacuum  chambers  with  other  similar 
data.     Volume  ratio  v/V =0.064;  temperature  200. 


Observed. 

Computed* 

Observed. 
ri-'i  =  273     t'-*2~273 

P- 

P'- 

Pz- 

t#V 

Pv 

p2. 

p\. 

XP"r 

K 

ft 

76 

43 
39 
42 

43 
45 
47 
5i 
53 
55 
57 
59 
43 
43 

0 

5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 
5 

454 
42.2 
45-2 
45-5 
47-3 
48.9 

52.5 
54-3 

580 
59-7 
45-7 
45-4 

48.0 
45-2 
47-9 
47-9 
49-3 
50.9 
54-3 
56.1 

59-8 
62.2 
48.4 
48.0 

45-7 
45-7 
52.4 

59-4 

52 
58 

63 

9 

3 

8 

45-0 
52.1 

59-4 

45-6 
47-4 
48.9 

_20.2° 

-  9-9° 

".2° 

24-3° 

2^5° 

20°" 

*  Checked  p' 2 +  p2v/V  =  p3  (i  +  v/V). 

t  Observed  as  soon  as  possible  at  the  fog  chamber.    Nearly  same  later. 

t  Observed  as  soon  as  possible  at  the  vacuum  chamber.     v"\  =»  Pz  nearly. 

The  data  of  table  17  are  computed  for  dry  air  throughout  and  are 
given  in  fig.  27a,  graphically.*  The  results  of  the  table  are  very  impor- 
tant. In  the  first  place,  it  will  be  seen  not  only  that  isothermal  pressures 
or  nearly  isothermal  pressures  are  not  observed,  but  that  the  effect  of  the 
vacuum  chamber  is  preponderating.  Thus  the  pressure  at  the  latter 
(p'\)  read  off  as  soon  as  possible  and  nominally  adiabatic  is  within  1  mm. 
of  pz.   Similarly  the  computed  adiabatic  pressure  (pt)  is  within  a  few 


♦The  curve  (p2)  is  of  no  interest  here  and  should  be  disregarded. 


EQUATIONS    OF    FOG    CHAMBER.  55 

millimeters  of  p'\  and  p3.  It  follows,  therefore,  that  even  an  approach 
to  isothermal  pressure  can  not  be  discerned  at  the  fog  chamber  at  all, 
to  say  nothing  of  adiabatic  pressure;  or  that  before  the  exhaust  cock 
can  be  closed  again,  the  vacuum  chamber  has  practically  regained  its 
isothermal  pressure  by  cooling  and  that  the  fog  chamber  is  further 
exhausted  by  a  corresponding  amount.  The  pressure  p\=p"2  observed 
under  isothermal  conditions*  at  the  fog  chamber  exceeds  px  (computed) 
by  about  1.9  cm.  on  the  average,  which  might  be  regarded  as  the  average 
vapor  pressure  of  water  at  the  temperature  at  which  the  observation  was 
made.  Leaving  this  for  further  consideration,  the  final  result  of  impor- 
tance is  the  following:  p2,  the  computed  isothermal  pressure  in  the 
closed  fog  chamber,  is  from  2  to  5  cm.  above  the  observed  (nominally) 
isothermal  pressure  p\—p2  (observed),  and  correspondingly  more  than 
this  above  the  common  isothermal  value  (p3)  usually  taken.  For  the 
region  in  which  colloidal  nuclei  lie  the  correction  will  be  in  excess  of 
the  difference  between  the  pressure  regions  containing  Wilson's  data  for 
colloidal  nuclei,  as  reduced  elsewhere,!  and  the  region  in  which  my  own 
data  as  summarized  below  would  lie.  In  other  words,  the  data  in  my 
large  coronal  apparatus  lie  in  regions  of  exhaustion  at  least  as  moderate 
as  those  observed  in  Wilson's  small  apparatus;  or  the  two  types  of 
apparatus  compare  in  efficiency  if  the  drop  of  pressure  taken  is  not  the 
apparent  experimental  value  but  that  deduced  for  the  computed  isother- 
mal pressure  (p2)  of  the  fog  chamber,  as  above  explained. 

47.  The  same,  continued.  Case  of  air  in  the  fog  chamber  saturated 
with  water  vapor. — It  will  next  be  necessary  to  compute  the  above 
data  with  allowance  for  the  vapor  pressure  of  water  in  the  fog  chamber, 
supposing  the  vacuum  chamber  to  be  dry,  which  may  seem  to  be  in  a 
measure  true,  since  it  is  heated  by  the  same  transfer  of  air  which  cools 
the  fog  chamber.  Hence  in  the  summary,  if  n  is  the  vapor  pressure  of 
water,  the  equations  relating  to  the  fog  chamber  have  to  be  modified  to 

p^n\(k-c)/k 


T,       \pi-nj 


p  —Ti  =Rpz 

px~~  Xl  =  RpiTl 
P2—7T   =  Rp2T  =  RplT 

p3-n  =Rp3z         p3  =  p'3  =  RP'3z3         pv+plV  =  etc.=p3v+p\V 

*This  pressure  varies  but  slightly. 

t  Presidential  address,  Physical  Review,  xxn,  1906,  p.  107, 


56 


VAPOR    NUCLEI    AND    IONS. 


From  these  the  value  of  pi  appears  as 


c/k  = 


P*+(P»-*)-v/V 


p^k-c)/k^(p-n){k-c)/k^  -njpjc/h  .  v/v 

where  nj pt  occurring  with  the  factor  v/V  may  be  neglected  Further- 
more 

8 (p2-  7z)  =  (p-7t)(k-c)/k(p1-7:l)c/k;  p' 2  =  pl(k-c)/k  Pic/k 

where  %t  (respectively  7r  =  0.10,  0.24,  0.51  in  comparison  with  pt  =  45.6, 
52.2,  59.3)  may  again  be  neglected. 

The  results  of  this  computation  are  given  in  table  18  and  fig.  276. 

Table  18  also  contains  the  value  of  dp  observed  as  p-pz  and  computed 
as  p-p2,  the  latter  being  the  correct  value.  This  table  of  corrections 
will  not  apply  below  the  limits  of  computation,  since  rcl  now  becomes 
appreciable  in  comparison  with  px ;  but  above  p-p3  =  1 5  cm.,  a  table  may 
be  constructed  from  which  dp=p-p2  may  be  taken  at  once.  In  this 
way  the  following  data  will  be  corrected  Since  the  main  data  for  col- 
loidal nuclei  lie  between  £-£3  =  25  cm.  and  32  cm.,  the  correction  will 
lie  between  -4  cm.  and  -6  cm. 


Table  18,  corresponding  to  table  17  for  saturated  moist  air  in  the  fog  chamber.    Tem- 
perature 200;  vapor  pressure  1.7  cm.;  £  =  76;   v/V  =0.064. 


dp. 

Observed. 

Computed. 

P~p3- 

P-Pr 

ft'. 

ft. 

*/>/• 

t/V'- 

ft. 

ft. 

ft*. 

Tj. 

*v 

30.5 
23-5 
16.3 

25.2 
19.9 
14.4 

43-5 
51-5 
59-5 

45-5 
52.5 
59-7 

47-9 
54-3 
62.  2 

45-6 

45-6 
52.2 

59-3 

50.8 
56.1 
61.6 

44.9 
52.0 
59-3 

-18.7 
~    8.5 
+     1.5 

+  24.0 
21 . 2 
+  20 

*  Observed  as  soon  as  possible  at  the  fog  chamber;  nearly  same  later, 
t  Observed  as  soon  as  possible  at  the  vacuum  chamber;  P\"=Pz  nearly. 

Table  19. — The  results  are  for  ir  =  1 .7  at  200. 


p- 

/>'. 

ft. 

ft. 

v/V -i. 

v/V"  =0.064. 

v/V-O. 

76-lr 

43-5 
59-5 

45-5 
52.5 
59-7 

48.1 

54-4 
60.7 

50.8 
56.1 
61.6 

53-i 
58.4 
63-7 

EQUATIONS    OF    FOG    CHAMBER. 


57 


Fig.  27a. — Computed  pressures  in  the  fog  chamber  and  in  the  exhaustion  chamber 
for  atmospheric  pressure,  p  in  the  former  and  p'  in  the  latter.     Dry  air.     Table  17. 

Fig.  276. — Wet  air  in  the  fog  chamber.     Table  18. 

Fig.  28. — Isothermal  pressure  in  the  isolated  fog  chamber  for  different  volume  ratios 
(v/V)  of  the  fog  chamber  and  vacuum  chamber.     Table  19. 


5» 


VAPOR    NUCLEI    AND    IONS. 


It  may  be  of  further  interest  to  compute  the  values  of  p-p3  for  v/  V  =  i 
(a  small  exhaustion  chamber)  and  for  v/V  —  o  (one  of  immense  size) 
for  the  same  values  of  p,  p',  p3,  observed  isothermally  and  initially  at 
the  fog  chambers  and  vacuum  chambers  and  finally  when  both  are  in 
communication.     The  results  for  200  are  given  in  table  19,  page  56. 

These  data  are  charted  in  figs.  28  and  30,  to  a  first  approximation,  in 
terms  of  v/V  and  p3.  If  expressed  in  terms  of  p',  they  lie  nearly  on 
straight  lines,  as  do  the  above  values  of  p2  for  v/V  =  0.064.     The  large 


45  50  55  60  cm. 

Fig.  27c. — Wet  air  in  both  chambers.     Table  20. 


variation  between  v/V =  0  and  0.064  as  compared  with  the  small  one 
for  v/V  =  0.064  and  1.0  is  noteworthy.  Hence,  in  using  small  vacuum 
chambers,  the  observed  and  computed  p3  and  p2  lie  more  closely  together, 
but  other  disadvantages  supervene.     The  rate  of  variation 


9(v/V) 


1  -   (p/p')  (k-c)/k 


-  {p/p')(k-c)/k.v/V}2 
is  always  negative  and  proportional  to  p3  and  (p/p')(k'c)/k. 


EQUATIONS    OF    FOG    CHAMBER. 


59 


10  ZO  30  40  42  44  46  48  50  52 

Fig.  29. — Corrections  (p2  -  p3)  for  dp  =  p  —  pz.     Table  20. 

Fig.  30. — Isothermal  pressure  p2  in  the  isolated  fog  chamber  for  different  isothermal 

pressures  p3  of  the  communicating  fog  chambers  and  for  different  volume  ratios 

(v/V).     Table  19. 

48.  Case  of  saturated  air  in  both  chambers. — Here  all  the  pressures 
of  both  chambers  must  be  reduced  by  the  corresponding  pressure  of 
saturated  vapor,  except  p\  where  the  vapor  is  slightly  superheated. 
Omitting  this  the  equations  become 

10 (pi-n)  =  (p-n) (*_c)/*  (Pi  -7:1)c/k 

or  the  equations  again  take  the  original  form,  though  a  special  computa- 
tion is  needed,  since  a  different  initial  pressure  (p)  enters.  These  results 
are  given  in  table  20  and  in  fig.  29. 

Table  20. — Corresponding  to  table  18  when  both  fog  chamber  and  vacuum  chamber  are 
saturated.     v/V  =  0.064;  temperature  200;  £=76  cm.;  ir—1.7 


dp. 

Observed. 

Computed. 

P-P+ 

P~K 

y. 

& 

*/>',. 

Pi*v 

t/V 

/>'«• 

Ti- 

T2- 

30.5 

23-5 
16.3 

23-7 
18.2 
12.7 

43.5 
515 

59-5 

45-5 
52.5 
59-7 

47-9 
54-3 
62.  2 

43-5 
50.3 
57-3 

52.4 
57-8 
63-3 

45- 1 

52.2 

59-5 

-22.5 

-11. 5 
-    1-4 

*  Observed  as  soon  as  possible  at  the  fog  chamber. 
t(*,-ir)  +  -Jr(*-ir)-(i+ £)(*--) 


6o 


VAPOR    NUCLEI    AND    IONS. 


P-Pz. 

P~P2. 

Ratio. 

o 

O 

16.3 

12.7 

18.2 
23.5 

23.5 

18.2 

■ 

30.5 

23.7 

11.0 

14.2 

0.7745 


0.7782 


P-Pz. 

Correction.  Ratio 

0 

O 

16.3 

3.0 

23.5 

Mean 

0.776 

23.5 

5-3 

30.5 

6.8     "-** 

14.2 

0.226 


0.225 


Mean 
0.225 


In  view  of  the  low  temperature  (fj)  the  vapor  pressure  (7^)  may  be 
neglected  for  the  fog  chamber;  but  this  would  not  be  the  case  of  the 
vacuum  chamber,  where  n\  is  quite  appreciable.  As  the  result  of  this, 
the  march  of  pressures  in  the  vacuum  chamber  is  peculiar,  but  need 
not  be  considered  here,  where  p,  p',  p3,  and  p2  are  chiefly  in  question. 
The  difference  between  dp0  =  p  -  p3  as  observed  and  dpc  =  p  -p2  as 
computed  now  actually  vanishes  with  the  former  (see  fig.  29).  In 
other  words,  very  nearly 


±Z£l-  0.775,  or  tltl 

P~P3  P    ~P3 


0.225 


and  therefore  dp0-dpc  =0.225  dp0,  nearly.  Hence  this  is  a  correction 
to  be  taken  by  preference.  A  table  giving  0.225  dp0  for  the  usual  ranges 
of  observation  was  therefore  drawn  up  and  used  throughout  the  follow- 
ing work,  or  the  factor  0.775  may  be  used  at  once.  These  corrections 
are  quite  sufficient  to  indicate  that  the  efficiency  of  the  fog  chamber  as 
used  above  is  not  surpassed  by  any  apparatus. 

The  preceding  correction,  in  comparison  with  the  cases  of  sections  46 
and  47,  seemed  to  me  to  be  most  nearly  in  keeping  with  the  actual  state 
of  the  case.  The  more  nearly  rigorous  solution,  when  the  air  in  both 
chambers  is  continually  saturated,  leads  to  transcendental  equations  for 
the  adiabatic  pressures  (pi  —  p\),  which  can  only  be  obtained  approxi- 
mately. If  the  vapor  pressures  {nx  and  n' x)  correspond  to  px  and  p\, 
the  results  would  be 


(Pi-*\)e/k 


{px-nxY/h  = 


(/>,-*)  (1+1//V) 


(//-7r)(*-c)/*  +  v/V.(i-(w1-w,1)/(^1-w,1))c/*(p-7r)(*-c)/* 

(PS-7Z)   (I+V/V) 


(^An^-n^lip.-n^^Hp'  -^k-c)/k  +  vjV  .{p~n)(<k-cyk 


where  approximate  values  must  be  entered  for  n1 \,  7Tt,  pu  in  the  denom- 
inator on  the  right  side  of  the  equation. 


EQUATIONS    OF    FOG    CHAMBER. 


6l 


Similarly 

p2-x=(Pi-  ^i)c/k(P  ~  7r)(*-c)/&, 

ft  -  *=(p'i  -  n\YHp'  ~  *)W*, 

*/*-((*-*)/(*-*,))(**»/*      r/T/-(^/-3t)/(^/-*/))<^)/* 

Making  use  of  the  values  of  table  18,  the  data  of  table  216  were  com- 
puted on  a  single  approximation. 

Table  216.— Corresponding  to  table  18,  when  both  fog  chamber  and  vacuum  chamber 
are  saturated.     v/V  =0.064;  temperature  20°;  ir  =  i.7;  £=76  cm. 


*ir. 

*<• 

obs. 
P'- 

obs. 

h> 

p2. 

*V 

*« 

f%> 

OO 

2-3 

43-5 

45-5 

46.1 

54.7 

44-9 

-17.80 

+  24.10 

.2 

1-9 

51-5 

52.5 

52.5 

59-6 

52.0 

-    8.3 

21.3 

•5 

1-7 

595 

59-7 

59.3 

64.6 

59-4 

+      .8 

19.8 

♦Assumed  from  data  for  t\ ,  iT\,  in  table  18. 


P-Pz- 

P~Pr 

(P-PJAP-P*)- 

IT. 

irV 

h- 

Pi/ Pi- 

?r 

0.0 

16.3 

23-5 
30.5 

0.0 
1 1.4 
16.4 
21.3 

16.4 

-2£-   .69 
14.2 

O.7 
9 

2.2 
i-9 
1-7 

+    5-2 
+   9.4 
+  12.7 

0.910 
.929 
•952 

499 
55-5 
61.5 

The  corrections  (see  table  216,  and  upper  graphs  in  fig.  30)  again 
lie  on  a  curve  which  passes  through  zero,  but  with  a  larger  slope.  In 
fact,  they  are  so  much  larger  than  the  preceding  cases  and  throw  the 
whole  phenomenon  into  so  low  a  region  of  pressures  that  it  has  seemed 
best  to  abide  by  the  data  at  the  beginning  of  this  paragraph,  at  least 
for  the  present.     Details  are  given  in  table  216. 

A  few  incidental  results  deserve  brief  attention.  The  first  of  these 
is  the  nearly  constant  difference  of  about  dp2  =  2  cm.  between  the  ob- 
served value  of  p2  (nominal)  and  p3.     Since  for  dry  air  or  not 

(p'2-7t)+v/V.  (p2-7:)  =  (pa-7:)(i+v/V) 

is  constant  for  a  given  exhaustion, 

dp'2  =  -v/V.  dp2. 
Hence  if  dp2  =  2  cm. 

dp'2  =  o. 064X2=0. 13  cm. 


62  VAPOR    NUCLEI    AND    IONS. 

The  case  is  illustrated  graphically  for  p'  =  45  cm.  in  the  notched 
curves  of  fig.  27c  in  a  way  easily  understood.  It  seems  probable  that 
whereas  the  smaller  fog  chamber  has  more  than  returned  to  isothermal 
conditions  (p2),  the  large  vacuum  chamber  is  about  a  millimeter  short 
of  it  when  the  cock  is  again  closed.  The  constancy  of  this  difference 
is  in  all  probability  referable  to  the  systematic  method  of  investigation, 
though  the  effect  of  precipitated  moisture  has  not  yet  been  considered. 

Anomalous  relations  in  the  data  for  the  fog  chamber  (as  in  the  case 
of  ^  =  59.5  cm.)  are  direct  errors  of  observation.  On  the  other  hand, 
however,  since  within  the  ranges  of  observation  and  very  nearly 

p  =a 

p2=a2+b2p' 
p3=a3+b3p' 
(P ~ P%) /(P-Ps)  =  (As+ Bzp') /(A2  +  B2p')  =A+Bp'  (nearly) , 

where  a,  b,  A,  B,  etc.,  are  constant.    Frequently  B  is  negligible,  so  that 

(£-£2)/(£-£3)=^  =  const., 

in  which  case  the  graph  for  (p2-pa)/(p-p3)  —  i-A  also  passes  through 
the  origin  as  in  the  two  cases  (fig.  30).  There  is  no  need  of  this  and  it  is 
at  best  an  approximation  which  facilitates  computing. 

Some  remarks  may  here  find  place  on  the  moisture  precipitated  in  the 
fog  chamber  per  cubic  centimeter,  and  on  the  absolute  temperature  xx 
to  which  this  precipitation  heats  the  chamber  above  the  adiabatic 
temperature  zv  I  have  shown  above  that  the  combination  of  fog 
chamber  with  a  large  vacuum  chamber  and  a  sufficiently  wide  passage- 
way, though  affording  superior  practical  advantages,  and  little  if  any 
inferiority  in  efficiency  to  the  piston  apparatus  within  the  range  of 
measurable  coronas,  nevertheless  does  not  give  the  volume  expansion 
of  the  air  within  the  fog  chamber  either  under  adiabatic  or  under  iso- 
thermal conditions.  It  makes  no  difference  how  rapidly  the  stopcock 
is  manually  closed.  The  conditions  of  the  vacuum  chamber  are  always 
impressed  upon  the  fog  chamber.  The  adiabatic  and  isothermal  data 
may,  however,  be  computed  if  the  volume  ratio  of  the  fog  and  vacuum 
chambers  and  the  pressures  before  exhaustion  (when  the  chambers  are 
isothermally  separated)  and  after  exhaustion  (when  the  chambers  are 
isothermally  in  communication)  are  known;  and  these  computations  are 
simple  because  the  reductions  are  practically  linear. 

When  the  vacuum  chamber  is  large,  moreover,  its  pressures  vary  but 
slightly,  and  therefore  the  pressure  observed  at  the  vacuum  chamber 
after  exhaustion,  when  the  two  chambers  are  in  communication,  is  very 
nearly  the  adiabatic  pressure  of  the  fog  chamber.     This  result  makes  it 


EQUATIONS    OF    FOG    CHAMBER.  63 

easier  to  compute  the  water  precipitated  per  cubic  centimeter  (without 
stopping  to  compute  the  other  pressures)  with  a  degree  of  accuracy 
more  than  sufficient  when  the  other  measurements  depend  on  the  size  of 
coronas. 

To  prove  this,  let  d,  L,  and  n  refer  to  the  density,  latent  heat  of 
evaporization,  and  pressure  of  water  (or  other)  vapor;  let  p,  k,  c,  t, 
denote  the  density,  specific  heat  at  constant  pressure,  specific  heat  at 
constant  volume  and  temperature  of  the  air,  the  water  vapor  contained 
being  disregarded  apart  from  the  occurrence  of  condensation.  Let  the 
variables,  if  primed,  refer  to  the  vacuum  chamber,  otherwise  to  the  fog 
chamber.  When  used  without  subscripts,  let  them  refer  to  isothermal 
conditions  or  to  room  temperature.  Let  the  subscript  x  refer  to  the 
adiabatic  conditions  on  exhaustion;  the  subscript  2  to  isothermal  con- 
ditions, if  the  chambers  could  be  isolated  immediately  after  exhaustion 
and  allowed  to  heat  and  cool  from  the  adiabatic  state  independently. 
This  case  is  in  fact  realized  in  the  piston  apparatus.  Let  the  subscript  3, 
finally,  refer  to  the  isothermal  conditions  which  prevail  if  the  cham- 
bers are  put  in  communication  at  a  room  temperature  after  exhaustion. 
Then  the  usual  equations  for  heat  evolved  in  the  condensation  of  vapor 
lead  easily  to 

where  d  is  the  density  of  saturated  vapor  at  t,  where  t  is  the  tempera- 
ture to  which  the  wet  air  is  heated  from  its  adiabatic  temperature  tv 
in  consequence  of  the  condensation  of  water  vapor,  where  [dj  is  the 
density  of  water  vapor  if  cooled  as  a  gas,  i.  e.,  without  condensation, 
from  t  to  tv     Moreover 

[dj-df-m  (2) 

the  mass  of  water  precipitated  per  cubic  centimeter  by  condensation  or 
the  quantities  sought. 

If  Boyle's  law  is  assumed  to  hold  both  for  the  gaseous  water  vapor 
[dt],  and  for  the  wet  air,  it  is  convenient  to  reduce  equation  (i)  to  room 
temperature  (isothermal  state)  and  it  becomes 

If  the  vapor  density  of  saturated  water  vapor  is  known  at  a  temperature 
as  low  as  t, 

d=f  (T)  (4) 

so  that  t,  the  only  unknown  quantity  in  equation  (3),  since  the  equation 
of  adiabatic  expansion  determines  tv  is  found  from  the  intersection  of 
the  curves  (3)  and  (4).     This  is  the  method  of  Wilson  and  of  Thomson. 


64  VAPOR    NUCLEI    AND    IONS. 

In  the  piston  apparatus  p2  as  well  as  p  may  be  read  oft'  by  the  gages; 
but,  as  stated  above,  this  is  not  true  when  the  fog  chamber  communicates 
directly  with  the  vacuum  chamber.  In  this  case,  however,  px  is  nearly 
given  by  p3.  Consequently  it  is  expedient  to  reduce  equation  (i)  to 
the  adiabatic  conditions,  whence  (if  t  refers  to  absolute  temperature), 

<*=<*  (^r/k-^(^y/k(i-ti)     (5) 

Here  nv  the  vapor  pressure  at  tv  is  usually  negligible  (about  0.5)  as  com- 
pared with  pv  and  pt  may,  in  practice,  where  great  accuracy  is  not 
demanded,  be  replaced  by  p3,  which,  like  p,  is  read  oft  while  n  holds 
at  t,  which  is  also  read  off. 

In  illustration  I  will  give  a  numerical  example  taken  from  table  2 1  b 
where 


p  =  76  cm. 

Pz  -  45-5  cm. 

tx  =-17.8°  C. 

ir  =  1.7  cm. 

£1  =  46.1  cm. 

i    =5-25°  C. 

P  =0.00118 

/>2  =  54.7cm. 

*'1=24.I°C 

£'=43.5  cm. 

If  equation  (3)  is  taken 

?w=<;.36Xio"~6  grams  per  cubic  centimeter 
If  equation  (5)  is  taken 

w=5-35Xio-6 
If  equation  (5)  is  taken  and  px  replaced  by  p3 

w*=5-3oXio~6 

the  error  being  1  per  cent  of  the  true  value,  which  is  quite  near  enough 
in  practice  and  admits  of  easy  correction. 

Finally  one  may  compute  f2,  the  pressure  which  would  be  observed 
at  the  fog  chamber  instead  of  p2  if  allowance  is  made  for  the  water  pre- 
cipitated in  the  fog  chamber,  whereby  additional  air  escapes  into  the 
vacuum  chamber,  since  the  former  is  heated  from  Tito  zx.  The  chambers 
are  supposed  to  be  separated  (cock  closed)  immediately  after  conden- 
sation and  no  further  loss  of  air  is  to  take  place  from  fog  chamber  to 
vacuum  chamber  while  the  absolute  temperature  of  the  fog  chamber 
passes  from  ij  to  atmospheric  z.  Without  giving  the  full  discussion  for 
which  there  is  no  room,  I  will  merely  add  that 

P2-k  =  J-(Pi— *) 


EQUATIONS    OF    FOG    CHAMBER.  65 

where  7}  is  the  density  of  the  air  at  t,.     The  ratio  is  equal  to 

*  (ft-^i)(T1/T1  +  V^T,1/T1) 

if  the  vapor  pressures  7r  are  designated  like  the  temperatures  and  pres- 
sures with  which  they  are  associated.     Usually 

*        tl/Xt+v/V.-fJlTi 

suffices,  the  term  involving  the  vapor  pressures  (n)  being  a  correction  of 
about  1  per  cent.  The  computation,  to  which  I  shall  return  elsewhere, 
shows  that  p2,  computed,  is  always  above  p2,  observed,  so  that  the  fog 
chamber  begins  to  heat  itself  above  the  temperature  vt  before  the  cock 
can  be  closed  again  and  contains  less  than  its  normal  allotment  of  air. 
Thus,  in  the  example  given,  pi/pi  =  o.gi\  £2  =  47. 9,  observed;  and  p2  = 
49.9,  computed.  Hence  p  and  p3  alone  have  any  definite  meaning  for 
the  fog  chamber. 

49.  Observations  with  4-inch  exhaust  pipes. — The  observations  of 
this  paragraph,  apart  from  the  exhaustion  difficulties  already  discussed, 
were  made  peculiarly  difficult  by  the  unavoidable  leak  from  fog  chamber 
to  vacuum  chamber  through  the  large  exhaust  cock.  It  was  therefore 
essential  to  wait  many  hours  for  each  observation,  since  the  coronas 
corresponding  to  the  second,  third,  etc.,  of  successive  exhaustions  were 
smaller  than  the  first.  This  can  not  be  due  to  any  other  cause  than  the 
presence  of  water  nuclei  from  the  fog  of  the  first  exhaustion.  A  given 
corona,  moreover,  was  apt  to  decrease  in  aperture  as  much  as  one-half 
during  the  period  of  subsidence,  showing  growth  of  certain  particles  at 
the  expense  of  others,  the  latter  being  afterwards  detected  in  the 
water  nuclei  specified.  This  must  also  be  attributed  to  the  continued 
slow  exhaustion  due  to  the  leak  in  question. 

In  table  21  and  fig.  31  the  earlier  data  with  4-inch  pipes  are  given, 
chiefly  with  the  object  of  direct  comparison  with  foregoing  results  with 
2 -inch  pipes.  The  meaning  of  the  data  is  clear  from  the  earlier  tables, 
and  the  dp  here  mentioned  is  the  isothermal  value  observed  at  the  fog 
chamber  as  heretofore. 

On  March  16  to  18  the  data  are  irregular  in  the  way  common  to 
observations  in  a  newly  adjusted  apparatus.  The  effective  nucleation 
is  too  small  from  the  presence  of  interior  sources  of  relatively  bulky 
nuclei.  A  fairly  complete  series  was  undertaken  on  March  19.  The  out- 
going and  incoming  branches  do  not  quite  coincide,  and  the  data,  as  a 
whole,  still  lie  below  the  corresponding  results  with  2 -inch  exhaustion 
pipes.     This  is  indicated  in  fig.  31.     Of  later  observations  (March  22), 


66 


VAPOR    NUCLEI    AND    IONS. 


25  30 

Fig.  31. — Nucleations  (w)  observed  in  dust-free  air  and  dust-free  X-air  at  differ- 
ent exhaustions  (dp);  4-inch  pipes.     Table  21. 


DISTRIBUTIONS    OF    NUCLEI. 


67 


Table  21. — Colloidal  nuclei  in  air.    New  apparatus.    Glass  fog  chamber.    Piping 
12  inches  long,  4  inches  in  diameter;  4-inch  plug  stopcock. 


I. 

Mar.  16 
Later .  . 


II. 
Mar.  17 


Later . 


III. 

Mar.  18 


IV. 
Mar.  19 


Incom- 
ing se- 


Ob- 

served 

dp. 


25-4 
25.4 
25-4 
29.0 
29.0 

20.4 

251 
25.1 

29 

29 

29 

33 

33 

33 

38 

38.0 

42 

42 

33-5 

33-5 

33-5 

33-5 


33-5 


3i-5 
30.0 
28.2 
27.2 
26.5 
24.1 
22.6 
20.6 
19. 1 
17-5 


■7.2 


Cor. 


w  y' 

w  y 

w  y 

wB  P 

wy' 
w  o 
w  y 

gyo 

cor 
w  o 

gyo 

w  pcor 
w  o 
cor 

y'obg 

Stone- 
blue 
w  y 

gyo 

gBP 
b'  B 
gBP 

gyo 

togB 
gBP 
wog 

cor 

cor 

cor 

cor 

cor 

cor 

cor 

cor 


nxio- 


20 

3 
20 
2i6 

27 


o 

12 

25 

5i 

20 

28 

140 

3i5 

3i5 

165 

330 

35o 

350 

425 

30 

3i5 

425 
190 

3i5 

4i 

390 


540 
510 
500 
4425 

460 
300 
40 
18 
14 
13 
12 
10 

7 
2 


Ob- 

served 

s. 

Cor. 

dp. 

Incom- 

16.5 

Rain 

ing  se- 

151 

Rain 

ries. 

Later . .  . 

16.5 

Just 
seen 

Outgo- 

17.8 

0 

No 

ing 

corona 

series 

19. 1 

0 

No 

after 

corona 

several 

21 . 1 

2.2 

cor 

hours' 

23.1 

3-6 

cor 

rest. 

25.0 

3-1 

cor 

26.5 

3-7 

cor 

28.2 

7-i 

wyg 

30.3 

9-7 

wog' 

32.1 

11 

wybg 

32.8 

12 

gBP 

nx  10-3. 


Promiscuous  results. 


V. 
Mar.  20 
Later . . . 


VII. 

Mar.  22 


Later . . 

X. 

X-rays ; 

Z?  =  20 

cm. 


529.8 

gBP 

30.0 

yobg 

30.3 

gBP 

28.0 

gyo 

27 -3 

11 

wr'g 

26.2 

wpcor 

28.6 

•6.9 

gBP 

26.3 

4-5 

cor 

27.4 

5-5 

cor 

29.9 

10 

yobg 

33-9 

11 

gBP 

33-8 

11 

gBP 

32.7 

gyo 

33-6 

„ 

gBP 

30.6 

11 

gBP 

27.9 

11 

gBP 

25-3 

11 

gBP 

21.7 

5 

cor 

21.6 

50 

cor 

22.5 

10.5 

wrg' 

23-5 

gyo 

22.8 

5-o 

cor 

22.6 

10 

wyg 

21.5 

3-6 

cor 

21.6 

3-7 

cor 

o 
o 

3 
16 

9 
19 
120 
270 
390 
470 


450 
37o 
450 
390 
250 
165 

120 

33 
62 

330 
475 
475 
420 

470 
455 
430 
400 

39 

39 
210 
340 

40 
310 

16 


1  «=  3.8  persistently  except  on  first  exhaustion. 

2  Many  periods  follow. 

'Blurred;  other  coronas  very  clear,  often  multi- 
annular. 


4  Periods  usually  omitted. 

•Fog  chamber  greasy. 

•  Followed  in  next  exhaustion  by  small  corona. 

7  Apparatus  cleaned  again. 


68 


VAPOR    NUCLEI    AND    IONS. 


400 


300 


ZOO 


too 


Fig.  32. — Nucleations  (n)  observed  in  dust-free  air  and  dust-free  X-air 
at  different  exhaustions  (dp);  4-inch  pipes.     Table  23. 


DISTRIBUTIONS    OF    NUCLEI. 

Table  22. — Systematic  work.     Third  cleaning  of  apparatus. 

p  =  76  cm. 


69 

Isothermal  dp=*p—p3; 


dp. 

s. 

Cor. 

n  x  10-3. 

dp. 

s. 

Cor. 

n  X  io-*. 

I. 

VII. 

Mar.  26 

24.8 

3-4 

cor 

13 

Mar.  30 

30- 5 

11.5 

yobg 

330 

24.8 

3-8 

20 

30.5 

10.7 

wog 

300 

24.8 

3-9 

20 

28.8 

6.5 

wrg 

100 

26.6 

3-9 

cor 

21 

29.6 

10.5 

wrg 

25 

28.7 

4.0 

23 

33-0 

13 

gBP 

470 

304 

4-7 

42 

Later . . . 

32.2 

12 

gBP 

460 

31.2 

5-2 

w  b  r 

56 

VIII. 

32.2 

8.6 

w  p 

215 

Mar.  31 

30.8 

"•5 

gBP 

460 

II. 

30.8 

12.5 

gyo 

410 

Later .  .  . 

33-4 

13 

gyo 

425 

29.6 

".  5 

r  y°g 

355 

33-4 

9-5 

w  p  cor 

240 

27.7 

5-2 

wr 

50 

33-4 

11. 5 

wybg 

390 

IX. 

33-4 

9-5 

w  b  r 

250 

Apr.     1 

312 

12 

gBP 

460 

304 

8-7 

wpcor 

210 

312 

13 

gyo 

410 

28.8 

50 

cor 

46 

Later . . . 

30.6 

12 

gyo 

410 

26.8 

3-5 

cor 

15 

30.1 

n 

wybg 

375 

251 

2.7 

cor 

7 

X. 

22.0 

2. 1 

Faint 

2 

Apr.     2 

30.7 

12 

gy  0  bg 

410 

cor 

30.6 

12 

y'gbg 

380 

III. 

30.6 

7.8 

w  b  r  b 

180 

X-rays 

21.5 

3-8 

cor 

18 

XL 

from 

23-7 

11 

Vague 

345 

Apr.     3 

29.4 

7-7 

wPB 

147 

D=20 

gyo 

29-5 

5-8 

cor 

74 

cm. 

22.6 

4.4 

cor 

27 

XII. 

Vague 

Apr.    4 

297 

n 

yobg 

300 

22.5 

6.7 

gBP 

124 

29.6 

n 

wog 

300 

22.6 

8.7 

wp  cor 

175 

28.8 

8.8 

wPB 

220 

25.5 

gFog 

400 

29.0 

28-3 

wP? 

175 

IV. 

28.0 

6.0 

cor 

80 

Mar  27, 

'30.5 

gyo 

410 

XIII. 

2d  day. 

316 

10 

yobg 

380 

Apr.     6 

33-9 

3i3 

gBP 

470 

29.1 

10 

wog 

145 

26.5 

3-9 

cor 

22 

V. 

26.9 

3-9 

cor 

22 

Later . . . 

31.0 

12 

gyo 

410 

27.6 

5-2 

cor 

52 

30-4 

4.8 

cor 

45 

28.8 

8-9 

wP 

215 

29.4 

7-4 

wp 

145 

27.6 

7-3 

w  y 

120 

28.7 

5-8 

cor 

72 

XIV. 

28.0 

5-o 

cor 

46 

Apr.     7 

27-5 

7-4 

wrg 

120 

27.1 

3-3 

12 

27 -5 

cor 

28.0 

4.2 

27 

27-5 

5-2 

cor 

52 

28.8 

6.0 

w  y 

80 

XV. 

27.6 

5-i 

cor 

49 

30.0 

7.2 

wB  P 

150 

Apr.     8 

27.2 

22.7 

cor 

7 

30.6 

8.1 

wP  cor 

180 

27.0 

3-5 

cor 

15 

3i.4 

7.0 

w  y 

130 

26.9 

43-5 

cor 

15 

32.0 

11 

gy 

4i5 

25-5 

3-o 

cor 

15 

33-8 

gBP 

475 

Series 

VI. 

Apr.    8 

Mar.  28, 

34  -o 

13 

gBP 

470 

(55) 

25- 2 

i-3 

cor 

i-5 

3d  day. 

32.0 

13 

gyobg 

4i5 

(56) 

27.1 

2.6 

cor 

6.4 

30.5 

12 

wybg 

380 

(57) 

28.9 

5-9 

wrg 

78 

29.8 

8.0 

w  b  r  b 

180 

(570 

8.4 

wP  cor 

210 

28.8 

6-5 

wrg 

no 

(59) 

32.5 

12.5 

wyg 

390 

28.0 

4.1 

cor 

24 

XVI. 

27.0 

4.1 

cor 

24 

Apr.  10 

Later.  .  . 

305 

10.6 

yog' 

330 

(58) 

32.0 

13 

gBP 

460 

28.7 

6-3 

cor 

88 

30.8 

13 

gyo 

455 

27.1 

3-4 

cor 

14 

XVII. 

256 

3-4 

cor 

H 

Apr.  13 

30.0 

10.5 

wrg 

255 

VII. 

30.6 

9-5 

wrg 

240 

Mar.  29, 

30.3 

yobg 

330 

Apr.  14 

307 

12.5 

ygbg 

380 

4th  clay. 

30.6 

1 1 

yobg 

33o 

30.6 

n-5 

wog 

300 

30.6 

9-4 

wcg 

230 

Apr.  15 

30.9 

13- 

gytog 

455 

7° 


VAPOR    NUCLEI    AND    IONS. 


while  there  is  evidence  of  slight  improvement,  irregularities  are  at  times 
increased.  The  final  data  in  the  table  relate  to  the  effects  of  X-rays  from 
short  distances  (D  =  2o  cm.  to  anticathode) ,  and  the  peculiar  feature  here 
is  the  steepness  of  the  line  as  compared  with  earlier  results.  The  reason 
is  in  part  due  to  the  admission  here  of  dp=p-p3  instead  of  the  observed 
dp  as  heretofore,  the  effect  being  to  displace  upper  observations  rela- 
tively more  to  the  left.  It  is  already  quite  clear,  however,  that  neither 
for  X-air  nor  for  ordinary  air  have  the  earlier  data  been  much  improved. 
The  highest  corona  attained  in  both  cases  is  again  the  green-blue-purple 
type. 

Table  23. — Atmospheric  air.  Two  observations  daily.  Water  nuclei  removed  by  low 
exhaustion.  dp  =  p-  pz.  Aug.  diameter  s/30  nearly.  Fog  chamber  40  cm.  from  eye, 
250  cm.  from  light. 


Date. 

Observed. 

Computed. 

dp. 

s. 

Cor.        n ) 

<IO 

-1       p-p,. 

n  X  io-3. 

May    17 

30.6 

gBP 

*5o 

23-7 

385 

30.8 

12 

gBP 

150 

23-9 

385 

May    19 

29.0 

I  I 

wyog 

320 

22.5 

270 

May    20 

28.8 

I  I 

wr  0  g 

290 

22.3 

245 

May    19 

27.2 

4-2 

cor 

27 

21. 1 

22 

May    21 

27.4 

3.6 

cor 

18 

21.3 

15 

May    22 

27.1 

2.9 

cor 

8 

21.0 

7 

Mar.  24; 

33-6 

gBP 

26.0 

410 

X-rays 

30.6 

gBP 

23-7 

385 

from  D 

27.9 

gBP 

21 .6 

360 

=  20. 

25-3 

gBP 

19.6 

335 

21.7 

5 

cor 

16.8 

32 

21.6 

50 

cor 

16.7 

32 

22.5 

10.5 

wrg' 

17.4 

175 

23-5 

gyo 

18.2 

290 

22.8 

5-o 

cor 

17-7 

34 

22.6 

10. 0 

wyg 

17-5 

260 

21.5 

3-6 

cor 

16.6 

13 

21.6 

3-7 

cor 

16.7 

14 

Mar.    26 

21.5 

3-8 

cor 

16.6 

15 

23-7 

11 

gyo 

18.3 

290 

22.5 

6.7 

gBP 

17.4 

105 

22.6 

8.7 

wp  cor 

17-5 

145 

25-5 

gfog 

19.8 

335 

50.  Observations,  continued. — In  the  experiments  of  table  22  much 
difficulty  was  experienced  with  the  apparatus,  as  the  use  of  oil  with  the 
large  stopcock  was  often  liable  to  show  itself  in  the  blurred  walls  of  the 
fog  chamber  whenever  this  was  wetted  with  water.  It  is  usually  suffi- 
cient to  heat  these  walls  gently,  in  order  to  evaporate  the  suspicion  of 


DISTRIBUTIONS    OF    NUCLEI.  7 1 

an  oil  film  which  has  here  collected,  after  which  the  walls  remain  clear  for 
some  time  on  wetting.  Prior  to  the  systematic  investigation  of  table 
23, however,  the  apparatus  was  thoroughly  overhauled  and  cleaned.  The 
dp  referred  to  is  henceforth  to  be  p-p3,  i.e.,  the  difference  between 
atmospheric  pressure  and  the  pressure  (p3)  observed  when  fog  chamber 
and  vacuum  chamber  are  in  communication  at  the  given  temperature. 
Some  time  having  elapsed  since  the  last  observation,  the  first  experi- 
ments (parts  I,  II,  etc.)  of  the  tables  show  low  nucleation,  due  to  the 
presence  of  large  nuclei  originating  internally,  as  already  specified. 
Series  III,  with  X-rays,  agrees  very  fully  with  the  preceding  cases 
(table  22)  and  there  is  nearly  the  same  steepness  of  curve  (dp  =  p-  p3) 
already  instanced.  Conformably  with  this,  series  IV,  V,  etc.,  also  show 
increased  steepness  of  curve,  the  nucleation,  moreover,  being  higher 
because  the  interior  sources  of  relatively  large  nuclei  have  been  gradually 
removed.  But  there  is  throughout  much  irregularity,  and  periods  are 
frequent.  Remembering  that  above  the  dp  referred  to  is  the  drop  of 
pressure  observed  in  the  fog  chamber,  while  at  present  dp=p-p3,  a  slight 
advance  of  the  highest  nucleations  over  the  preceding  cases  is  discernible. 

51.  Observations,  continued. — In  table  24  observations  are  recorded, 
made  once  or  twice  a  day,  far  enough  apart  to  allow  water  nuclei  to 
vanish  by  time  loss.  After  each  measured  corona  a  low  exhaustion  was 
(as  usual)  made  to  remove  the  greater  number  of  such  nuclei  at  once  in 
the  large  particles  of  the  small  corona  produced.  The  pressure  difference 
(dp)  is  again  p-p3,  as  explained  in  section  48,  so  that  the  correction 
there  adduced  may  be  applied.  The  fog  chamber  was  rigorously  tight  as 
regards  the  influx  of  external  air,  but  air  flowed  slowly  from  fog  cham- 
ber into  the  vacuum  chamber,  through  the  leaky  stopcock.  Between 
the  exhaustions  the  air  was  kept  at  low  pressure  for  about  ten  hours,  and 
new  air  was  admitted,  just  before  exhaustion,  through  the  filter  into  the 
fog  chamber,  until  the  barometer  pressure  had  been  reached.  As  the 
whole  apparatus  had  been  left  standing  a  long  time,  dust-free  air  only 
was  present  in  the  fog  chamber  and  vacuum  chamber.  The  walls  of  the 
former  were  rubbed  clean  before  beginning  the  work. 

The  table  also  contains  the  above  data  for  air  energized  by  the  X-rays 
with  anticathode  distant  20  cm.,  observations  being  made  while  the 
radiation  acted  and  immediately  after  the  exposure  began,  to  avoid  the 
presence  of  persistent  nuclei.  The  computed  values  for  the  drop  in 
pressure  (p-p2,  where  p2  is  the  computed  isothermal  pressure  in  the 
isolated  fog  chamber  alone),  and  the  corresponding  values  of  n,  are  also 
given.  The  nucleation  refers  as  usual  to  the  exhausted  fog  chamber.  The 
results  are  constructed  graphically  in  fig.  5$. 


72 


VAPOR    NUCLEI    AND    IONS. 


FIG.  3  3 

J> 

9j/S 

J/ 

Sp* 

/ 

s 

1 

I 

ml 

'• 

' 

i  f 

1 

H 

> 

71X103      J 

Jo 

zo 


85 


Fig.  33. — Nucleations  (n)  observed  in  dust-free  air  and  dust-free  X-air  at 
different  exhaustions  (dp);  4-inch  pipes.     Table  23. 


DISTRIBUTIONS    OF    NUCLEI.  73 

52.  Discussion. — The  new  curves  (fig.  33)  lie  nearer  together  for  the 
energized  and  non-energized  states  of  the  gas.  This  obviously  results 
from  the  correction  applied  to  the  observed  values  of  dp.  Neither  do 
the  graphs  ascend  as  highly  as  they  did  before,  for  the  same  reason, 
remembering  that  the  nucleation  (n)  always  refers  to  the  exhausted  fog 
chamber.  Again,  the  new  curves  must  be  steeper  than  the  old;  but  both 
of  them,  i.e.,  the  curves  for  the  non-energized  and  for  the  energized 
gas,  have  about  the  same  slope,  so  far  as  can  be  made  out  for  the  case 
of  such  steep  curves  as  those  under  consideration.  Nevertheless,  it  is 
probable  that  there  is  some  other  reason  implied  in  this,  which  is  yet 
to  be  made  out.  For  the  ionized  state  the  observations  frequently 
suggest  a  kind  of  saturation  beyond  which  the  ions  pass  into  per- 
sistent nuclei  very  much  as  a  vapor  condenses.  In  other  words,  a 
maximum  ionization  pressure,  determined  by  a  definite  number  of  ions 
per  cubic  centimeter,  which  can  be  approached  as  the  radiation  is 
more  and  more  intense,  but  not  exceeded,  is  a  useful  conception  in  con- 
nection with  many  of  the  experiments  given. 

53.  Summary. — The  general  summary  of  this  chapter  has  already  been 
given  in  sections  42,  43,  and  52,  particularly  in  the  former,  with  regard  to 
fig.  25,  and  need  not,  therefore,  be  repeated  here.  The  highest  order  of 
available  coronas  has  been  invaded  and  surpassed. 

It  appears  that  the  limits  of  efficiency  of  the  practical  fog  chamber 
with  rapidly  opened  plug  cock  have  been  reached  when  the  long  cylin- 
drical vessel  of  about  6,000  c.  cm.  is  exhausted  into  a  vacuum  chamber  of 
about  100,000  c.  cm.  through  a  pipe  not  less  than  5  cm.  in  bore  nor  more 
than  50  cm.  long,  with  a  stopcock  of  wider  diameter  (7  to  8  cm.)  inter- 
posed. To  test  this  again,  such  a  fog  chamber  was  adjusted  as  shown  in 
fig.  34  (V  vacuum  chamber;  F  fog  chamber;  G,  g,  gages  at  the  former 
and  the  latter,  the  whole  mounted  on  casters  to  admit  of  shaking  the 
water  in  F;  goniometer  attached  to  fog  chamber).  The  results  are  given, 
both  for  fog  chambers  Nos.  I  and  II,  in  tables  24  and  25,  with  correc- 
tions for  the  barometer  as  explained  in  Chapter  VI,  sections  100  and  101 , 
and  they  are  charted  on  a  small  scale  with  other  data  (table  23)  in 

fig-  35- 

The  graph  for  chamber  number  II  would  coincide  with  data  inferred 
from  Wilson's  colors  for  small  coronas;  but  for  large  coronas  it  actually 
lies  in  a  region  of  lower  exhaustion — to  which  however,  too  much 
importance  must  not  be  attached,  because  of  the  difficulty  of  identifi- 
cation. The  point  is  that  the  apparatus  of  2-inch  pipes  is  quite  the  equal, 
if  not  the  superior,  of  the  apparatus  with  4-inch  pipes,  in  the  region  of 
both  the  lower  and  higher  coronas.    Curiously  enough,  the  apparatus  I 


74  VAPOR    NUCLEI    AND    IONS. 

(4-inch  cock)  gives  an  excess  of  ions,  whereby  the  graphs  for  I  and  II  in 
the  region  of  lower  coronas  are  consistently  distinct.  I  will  pass  this  over 
here,  as  it  needs  additional  investigation. 

That  the  limit  of  efficiency  has  been  reached  for  plug-cock  apparatus 
is  specifically  proved  by  the  fact  that  the  same  large  green-blue-purple 


Fig.  34. — Disposition  of  apparatus  in  case  of  fog  chamber  (F)  and  vacuum 
chamber  (V  ),  connected  by  2-inch  pipes  and  2^-inch  stopcock. 

corona  terminates  the  observations,  no  matter  whether  the  nuclei  are 
relatively  large,  as  in  case  of  the  ions  and  intense  X -radiation,  or  relatively 
small,  as  in  case  of  the  colloidal  nuclei.  This  is  differently  proved  in  the 
work  with  alcohol,  in  Chapter  IV. 

It  is  somewhat  hard  to  understand  why  the  efficiency  should  terminate 
abruptly,  with  a  certain  number  of  nuclei  per  cubic  centimeter,  no  matter 


DISTRIBUTIONS    OF    NUCLEI 


75 


whether  large  or  small  nuclei  are  in  question.  One  should  expect  these 
conditions  to  depend  on  the  size  of  nuclei ;  but  (as  the  data  show)  even 
though  larger  numbers  of  nuclei  are  certainly  present,  they  are  devoid 
of  efficiency  beyond  the  limit. 


of 
6 

\lo.R.  Tab. 26,1. 
"    ».     »     "  ,2. 
"  I.      "     24. 

Mo.I.  Tab. 26, 3. 
"  " .     »       "  ,4. 

"omputed. 

/ 

f 

\  1 

.  c 

/ 

DUSl 

-FREE 

AIR 

B 

A 

/ 

FIG.  3  5 

TIX/O'5 

=p-p2 

l_£ 

'£ 

[•/' 

26 

Fig.  35. — Nucleation  (»,  in  hundred  thousands  of  nuclei  per  c.  em.)  observed  in  dust- 
free  air  and  in  energized  air  at  different  exhaustions.  dp  =  p-p2.  2-inch  and  4-inch 
pipes  and  perfected  apparatus  I  and  II.  Tables  23,  24,  and  25.  Ions  in  No.  I  con- 
sistently in  excess. 

Table  24. — Fog  chamber  and  vacuum  chamber  as  in  fig.  34,  joined  by  2-inch  pipes, 
2^-inch  plug  stopcock.    dp=  p  -  p3.     Final  series  for  comparison. 


dp. 

5". 

Corona. 

P~P2- 

ft  X  io-3. 

.y  cor- 
rected.* 

n  Xio~s 
corrected. 

I.     Barometer 

25-9 

3-2 

cor 

20. 1 

9-5 

3-4 

n. 6 

76.2 

26.9 

6.4 

wp'g 

20.8 

76 

6.6 

83 

27.4 

6.8 

gBP 

21  .  2 

120 

28.7 

10.  2 

wrg' 

22.2 

210 

29.4 

12 

yr 

22.8 

310 

30- 5 

13? 

gBP 

23.6 

380 

33-5 

13? 

gBP 

26.O 

410 

II.  Barometer 

24.9 

i-7 

cor 

19-3 

1.8 

1.3 

1 

4 

75-5 

25.6 

3-6 

cor 

19.8 

15 

3-2 

9 

9 

26.4 

5-6 

cor 

20.5 

53 

5-2 

42 

Table  2= 

. — The  same;  4-inch  stopcock,  apparatus  I. 

dp. 

j. 

Corona. 

P-Pv 

nx  10-8. 

s  cor- 
rected.* 

n  X  io~s 
corrected. 

III.  Barometer 
£  =  75-8, 
July  14. 

IV.  />  =  75-9, 
June   3. 

25 -5 
27.  2 
25.0 
28.1 

27-3 
27. 1 

25-9 
26.1 

27.4 

?3 
4 
2 

7 
5 
4 
2 
2 
5 

7 
9 
4 
2 

3 

2 
8 

7 
0 

cor 

y'  b  P 
cor 

19.7 

21  .  I 
I9.4 
21.8 
21  .  I 
21  .O 
20.  I 
20.  2 
21-3 

15 

37 

4 

no 

45 

22 

6 

6 

40 

3-6 

4.8 

2-3 

5-2 

*  Correction  for  barometer  made  as  explained  in  Chapter  VI. 


76  VAPOR    NUCLEI    AND    IONS. 

In  no  form  of  the  fog  chamber  have  the  initial  yellows  and  browns  of 
the  steam  jet  been  approached.  Coronas  reach  but  to  the  equivalent  of 
the  opaque  zone.  Below  the  large  green-blue-purple  corona,  the  com- 
puted value  of  the  water  precipitated  per  cubic  centimeter  may  now  be 
considered  trustworthy.  In  Chapter  I  this  was  true  below  the  middle 
green-blue-purple  corona.  The  drop  of  pressure  (p  -  p2)  actually  efficient 
in  producing  low  temperatures  in  the  fog  chamber  must  be  computed 
from  the  initial  pressure  of  the  isolated  fog  and  vacuum  chambers  before 
exhaustion,  and  their  final  pressure  when  in  communication  after  exhaus- 
tion, all  data  taken  at  the  same  temperature. 

As  the  intensity  of  radiation  increases,  coarser  nuclei  become  much 
more  frequent,  but  beyond  this  the  coronal  method  is  not  adapted  to  test 
the  lower  limit  in  question.  At  the  upper  limit,  however,  most  of  the 
observations  show  that  the  finer  nuclei  become  more  abundant  when  the 
medium  is  more  powerfully  energized ;  or  that  new  gradations  of  nuclei 
of  continually  increasing  smallness  and  continually  increasing  number 
are  produced  by  radiation  increasing  in  strength  indefinitely.  These  are 
important  questions,  however,  upon  which  I  hope  in  the  near  future  to 
make  some  final  tests. 


CHAPTER  III. 


MISCELLANEOUS  EXPERIMENTS. 


54.  Objects.— Having  perfected  the  coronal  fog  chamber  to  the  degree 
specified  in  the  earlier  sections  of  Chapter  II,  it  seemed  expedient  to  make 
use  of  it  for  a  variety  of  purposes  partly  corroborating  and  interpreting 
my  earlier  work,  partly  introducing  new  results.  In  particular,  the  growth 
of  persistent  nuclei  in  a  highly  ionized  medium  in  the  lapse  of  seconds, 
the  occurrence  of  solutional  nuclei,  and  like  questions  may  be  studied 
by  the  depression  of  the  terminal  asymptote  produced  by  the  introduction 
of  relatively  small  numbers  of  larger  nuclei  into  the  medium.  Again,  the 
effects  of  radiation  from  different  distances  on  the  medium  of  the  fog 
chamber,  the  absorption  of  such  radiations,  the  distributions  within  the 
fog  chamber,  etc.,  may  be  elucidated  by  this  treatment.  Finally,  some 
consideration  of  the  rates  of  generation  and  decay  of  ions  is  in  place  and 
a  method  will  be  shown  for  the  standardization  of  coronas.  Some  final 
remarks  will  be  made  on  the  steam  jet  and  on  the  relation  of  its  color 
phenomena  to  those  of  the  fog  chamber. 

Throughout  this  chapter  dp  refers  to  the  drop  of  pressure  observed  at 
the  isolated  fog  chamber  under  isothermal  conditions,  the  exhaust  cock 
being  closed  as  soon  as  possible  after  the  expansion.  The  necessary 
reductions  (should  they  be  needed)  may  be  made  as  shown  in  the  pre- 
ceding section. 

55.  Growth  of  persistent  nuclei. — In  table  26  (illustrated  by  fig.  36) 
the  time  during  which  the  fog  chamber  was  exposed  to  the  X-rays,  with 
the  anticathode  at  a  distance  of  D  =  io  cm.  from  the  fog  chamber,  is 
given  in  the  first  column.  The  coronas  and  the  number  (n)  of  nuclei 
per  cubic  centimeter  follow. 

The  two  series  of  experiments  made  show  that  there  is  a  gradual 
increase  of  the  number  of  persistent  nuclei,  evidenced  by  the  gradual 
reduction  of  the  number  of  efficient  nuclei.  In  less  than  two  minutes, 
however,  the  phenomenon  becomes  more  stationary,  indicating  that  the 
full  number  of  persistent  nuclei  is  being  approached,  or  that  there  are 
now  about  as  many  made  as  are  unmade  per  second.  It  is  difficult  to 
follow  the  phenomenon  beyond  this,  for  the  coronas  now  become  cam- 
panulate  or  otherwise  distorted,  appearing  in  association  with  heavy 
fogs.  The  true  asymptote  is  probably  far  off.  These  data  furnished 
good  illustrations  bearing  on  the  remarks  of  section  42,  Chapter  II. 

77 


7» 


VAPOR    NUCLEI    AND    IONS. 


Table  26. — Persistent  nuclei  produced  after  different  lapses  of  time.  Method,  depres- 
sion of  asymptote,  dp  =26.4  cm.;  D=»io  cm.  above  side  of  cylindrical  glass  fog 
chamber;  cock  i§  inches;  exhaustion  during  exposure. 


Exposure. 

s. 

Corona. 

n  xio-3. 

sec. 

0 

13 

gBP 

410 

30 

12 

wyg' 

340 

60 

II 

w  0  g' 

270 

1       90 

L  ,7-5 

O 

140 

§1    I20 

117-6 

0 

140 

If  i°o 

..  13  i 

m  1 1 1 

wyg' 
'wrg 

340 

230 

}     90 

mi9t 

0) 

200 

0 

$f   14  £ 

gBP 

410 

1  Tempestuous  fog  and  rain,  leaving  smaller  corona.    Second  exhaustion  made  for  safety,  showing 
small  corona. 


4O0**3 

*n? 

FIG. 

36 

s 

Ss, 

nxW3 

t 

1  0/stor{ 

'on 

L 

Exposi 

re  (sec.) 

80 


Fig.  36. — Depression  of  efficient  nucleation  (w)  of  dust-free  air  ionized  by  strong  X-rays 
at  a  given  exhaustion,  by  accumulation  of  persistent  nuclei  in  the  lapse  of  time- 
Table  26. 


56.  Water  nuclei  produced  by  evaporation. — A  beautiful  method  of 
demonstrating  the  production  of  water  nuclei  in  connection  with  the 
condensation  of  fog  consists  in  leaving  the  cock  for  influx  of  air  from 
the  filter  slightly  open.  In  such  a  case  the  fog  begins  to  evaporate  as 
soon  as  produced,  and  there  will  be  less  loss  from  subsidence  of  fog 
particles,  in  proportion  as  the  evaporation  is  more  rapid;  in  other  words, 
as  the  stopcock  is  more  widely  opened.  Table  27  shows  results  of  this 
kind  and  they  are  reproduced  in  fig.  37,  where  the  abscissas  are  dis- 
tributive. In  every  case  the  efficient  nucleation  (n)  of  dust-free  air, 
after  complete  subsidence  of  the  preceding  fog,  is  much  in  excess  of 
nf,  the  nucleation  observed  when  the  fog  is  dispelled  by  evaporation. 
The  table  also  proves  that  the  degree  to  which  the  filter  cock  (fine  screw 
valve)  is  open  does  not  influence  the  result. 


WATER    NUCLEI. 


79 


Table  27. — Enlargement  of  nuclei  of  dust-free  air.  Glass  fog  chamber,  single  wet 
cloth  partition.  op=  30.9  cm.;  s  found  after  complete  subsidence  of  preceding  corona ; 
s'  after  partial  subsidence  with  evaporation. 


Date. 

s. 

*'. 

Cock 
open. 

n  x  io~3. 

n'  x  10-3. 

s. 

n  x  io~s. 

Remarks. 

f  Full   subsi- 

Oct. 17 

»7.o 

37-o 

7.0 

5^8 

45 
45 

45 

45 

135 
135 

135 

76 

27-4 
7-4 
7-5 

140 
140 
140 

dence  but 
with  quick 
opening  of 
cock  (900) 
thereafter. 

f  Same,     but 

6.0 

45 

84 

7-4 

140 

with    slow 
influx. 

Oct.  19 

7-i 

45 

135 

7-3 

45 

150 

7.3 

55 

7 

45 
45 

150 

72 

474 

56 

2 

45 
45 

150 

88 

47-5 

63 

0 

90 
90 

150 

10 

27-2 

90 

140 

1  After  many  days'  waiting. 

lw  o  g. 

s  After  few  minutes'  waiting. 


<gBP. 

»  Blurred  with  much  rain. 


120 


100 


24  26  30 


Figs.  37  and  38. — Periodic  variation  of  efficient  nucleation  (n)  in  case  of  an 
open  filter  cock.     Tables  27  and  28. 


8o 


VAPOR    NUCLEI    AND    IONS. 


In  table  28  and  fig.  38  the  occurrence  of  periodic  variation  in  the 
angular  diameter  of  successive  coronas  and  the  corresponding  efficient 
nucleation  is  shown  by  the  same  method  of  a  permanently  opened  filter 
cock.  The  conditions  of  all  of  the  exhaustions  are  quite  identical;  but 
the  small  fog  particles  of  large  coronas  evaporate  faster  and  in  greater 
numbers  than  the  larger  particles  of  smaller  coronas.  Hence  the  water 
nuclei  are  present  in  like  periodic  distribution.  The  effect  is  more 
striking  when  the  stopcock  is  opened  wider.  The  difference  between 
1800  and  900  in  the  adjustment  of  the  cock  is  not  marked,  because  the 
filter  itself  introduces  resistance  to  flow. 

Table  28. — Corresponding  to  table  27.     Periodicity  due  to  permanent  open  filter  cock. 


s. 

sf. 

Cock 
open. 

n. 

n'. 

Oct.  20  .  . 

'6-5 

26.2 

J6.9 
26-4 
*7  1 

17-5 

32.8 
*7-2 

33-o 
47-2 

;7-4 

33.o 
x7.o 

32.9 

0 

45 

45 

45 

45 

45 

90 

90 

90 

90 

90 

180 

180 

180 

180 

180 

102 

89 
121 

96 
130 
150 

7.8 
150 

10. 0 
150 
150 

10 
130 

9 
130 

1  w  o  g.  3  Blurred  with  rain. 

2  w  r  g.     Note  the  periodicity  of  the  series.        4  g  B  p. 

Table  29. — Corresponding  to  table  27.     Effect  of  dp;  cock  open  during  exhaustion. 


Cock 

dp. 

s'. 

open. 

n' . 

Oct.  22 

26 

3.6 

0 
45 

17. 1 

26 

2.6 

45 

6-3 

26 

2.7 

45 

7-i 

28 

5-9 

45 

77 

28 

4-4 

45 

31 

28 

5-2 

45 

53 

30 

7.0 

45 

125 

30 

6.1 

45 

85 

30 

6.9 

45 

120 

30 

6.0 

45 

85 

30 

6.6 

45 

105 

7-3 

Closed 

135 

WATER    NUCLEI. 


8l 


In  table  29  the  effect  of  different  drops  of  pressure  (dp)  is  investigated 
for  low  exhaustions  and  smaller  coronas  and  there  is  scarcely  any 
periodicity.  As  the  exhaustion  is  higher,  periodicity  in  the  size  of 
successive  coronas  is  correspondingly  marked.  The  data  give  an  esti- 
mate as  to  the  degree  in  which  periods  are  to  be  guarded  against. 

In  table  30  experiments  similar  to  the  preceding  are  made  with 
ionized  air.  It  will  be  seen  that  the  periodicity  is  in  every  case  just  as 
marked  as  before.  In  the  absence  of  evaporation  (closed  filter  cock) 
the  successive  coronas  are  equal.  Precipitation  at  a  low  drop  (dp)  of 
pressure  is  followed  by  a  relatively  large  corona  at  a  higher  drop  of 
pressure,  as  the  water  nuclei  have  been  removed  in  the  former. 


Table  30. — Periodicity  of  ionized  air.     X-rays;  D  =50  cm.     Filter  cock  permanently 
just  open.     Kxhaust  cock  i\"\  dp  =  23  cm.  below  fog  limit  of  dust-free  air. 


Exp.  No. 

s. 

Cor. 

n  x  io~s. 

, 

10.5 

wrg 

210 

2 

6-3 

cor 

75 

3 

9.6 

wcg 

200 

4 

5-o 

cor 

4i 

5 

10.4 

wrg 

210 

6 

5-6 

cor 

58 

7 

9.2 

wcg 

190 

Filter  coc 

Ic  closed  ( 

luring  exhaustion 

and  sut 

>sidence. 

8 

'9.3 

wcg 

190 

Dust-free  air  not  e 

nergized;   dp  =31; 

repetitions  without  waiting  Dec.  13; 

internal  evolution  of  nuclei  has  ceased. 

115 

wyg 

335 

"•5 

wyg 

335 

Dust -free , 

air  not  ene 

rgized;  dp 

=36  cm. 

13-5 

g|  P 

480 

135 

g|P 

480 

Evap.  nuclei  precipi 

tated  at  dp  =23.2 

cm.  and  then  tes 

ted  at  dp  =31. 

1 

30 

cor 

8 

2 

0.0 



0 

3 

2gyo 

410 

No  difference  between  7  and  8. 


2  Corona  enlarged  by  the  preceding  precipitation. 


Some  interesting  questions  present  themselves  in  connection  with 
this  work.     Are  the  nuclei  holding  positive  ions  different  from  those 


82 


VAPOR    NUCLEI    AND    IONS. 


holding  negative  ions?  Do  they  retain  their  charges,  or  some  equiva- 
lent of  the  charges?  As  there  is  less  mobility  and  slower  recombina- 
tion in  cases  of  ions  entrapped  by  water  nuclei,  one  would  infer  greater 
opportunity  for  the  gravitational  separation  of  the  equivalents  of  the 
positive  and  negative  charges;  for  it  seems  improbable  that  the  water 
nuclei  resulting  can  be  of  the  same  size. 

Finally,  in  table  31  data  have  been  gathered  showing  the  gradual  self- 
purification  of  the  fog  chamber,  after  cleansing  and  sealing.  Nuclei 
arising  from  some  internal  source  cease  to  appear  in  the  mere  lapse  of 
time  and  without  further  interference.  The  coronas  s1  and  s2  are  observed 
in  successive  exhaustions  at  the  time  (days  and  hours)  given.  Initially 
the  first  corona  is  smaller  in  marked  degree,  owing  to  the  spurious 
nucleation  within.  After  more  than  three  days,  however,  both  coronas 
st  and  s 2  are  identical. 


Table  31. — Purification  of  the  fog  chamber  in  the  lapse  of  time.     dp  =  31, 
cock  2\  inches;  piping  12  inches  long,  2  inches  in  diameter. 


Exhaust 


Date. 

Hour. 

tx. 

Cor. 

s2. 

Cor. 

n,  xio~3. 

n2  xio-3. 

Nov.  30 

Dec.     1 

Dec.     2 
13 

10  a.  m. 

5  P  m. 
10  a.  m. 

6  p.  m. 



4.6 

7-5 
8.0 

*9-7 
9.2 

11  -5 

2i4 

gBP 
w  P  cor 

wcg' 

wrg 

wyg 

g' 

11 .5 
12.0 
11. 7 

11. 4 

11. 5 
14 

wyg' 
wyg' 

gyo 

w  0  g 
wyg 
g  i  P 

40 
150 

180 

275 
230 

305 
460 

305 
380 
380 
410 
305 
335 
460 

1  Vacuum  maintained  some  hours. 


1  dp=  36.     Internal  source  of  nucleation  absent. 


The  source  of  this  transient  internal  nucleation  is  difficult  to  detect. 
There  were  no  leaks.  Oil  evaporation  if  harmful  would  be  continuous. 
The  same  differences  of  fresh  and  stagnant  air  in  relation  to  st  and  s2 
are  always  reproduced.  There  is  no  evidence  that  anything  in  the 
vacuum  chamber  is  capable  of  diffusing  into  the  fog  chamber.  Some 
agency  therefore,  which  is  productive  of  relatively  large  nuclei,  and  the 
nature  of  which  is  not  clear,  survives  many  consecutive  precipitations. 


57.  Distance  effects.  X=rays. — In  the  following  experiments  I  endeav- 
ored to  overhaul  the  curious  results  obtained  when  the  X-rays  strike 
the  fog  chamber  from  different  distances,  without,  however,  reaching 
very  satisfactory  conclusions.  The  object  of  the  following  work  is  to 
bring  to  bear  the  newly  improved  means  on  the  problem.  In  table  33 
data  are  given  as  obtained  with  the  glass  fog  chamber,  the  drop  of 


DISTANCE    EFFECTS. 


83 


pressure  (dp)  being  below  the  coronal  fog  limit  of  dust-free  air.  Hence 
there  are  no  complications  from  colloidal  nuclei.  In  parts  I  and  II  of 
the  table  the  X-ray  bulb  was  not  inclosed  in  the  windowed  lead  vessel 
specified,  whereas  in  part  III  this  is  the  case;  while  in  part  IV  a  tin 
plate  has  been  placed  over  the  window. 


Table  32. — Distance  effects  due  to  X-rays.     Fog  chamber  of  glass  with  2.5-inch  gas 
cock  and  2-inch  piping  12  inches  long.     X-ray,  7  cells.     <?/>=  23.8  cm. 


I.  Bulb  not  inclosed;  meters 


D. 


0.5 
6.0 


10. o 

6.3 
6.2 

7-3 

74 

11 .0 


Corona,     n  Xio-3. 


wcg 
cor 

w;  B  P 
w'  B  P 

gyo 


220 
so 
75 
115 
120 
260 


=  20.3  cm. 


II.  Same;  bulb  not  inclosed 


0 

5 

w  B  P 

7 

2 

w  B  P 

2 

0 

5 
5 

2 
2 

6 

0 

S 

5 

5 

4 

0 

3 
4 

6 

5 

;;;;;; 

1 

0 

6 

4 

wr  g 

6 

3 

wrg 

5 

7 

2 

wyg 

7 

3 

wyg 

90 

100 

42 
42 

13 

«3 
15 

28 

75 

70 

100 

I  OS 


22.7 ;  X-ray  bulb  in  lead  case1  with  window  7.5  cm.  in  diameter. 


III.  Window  open 


Lid  off. 


600 

4.1 

cor 

400 

4.4 

cor 

200 

6.5 

wrg 

IOO 

7-5 

gBP  + 

7-5 

gBP  + 

7-5 

gBP  + 

22 

27 

85 

135 

135 

135 


Same.     Tin  plate1   over  window. 


IV.  Tin  window 


600 
200 
100 


2.7 
4-9 
6.9 


cor 

cor 

wrg 


6-5 
40 

99 


1  Lead  sheet  0.12  cm.  thick;  tin  plate  0.03  cm.  thick. 


84 


VAPOR    NUCLEI    AND    IONS. 


ZOO 


180 


!40 


JZO 


100 


80 


60 


40 


20 


\ 

X 

\ 

FIG. 

40 

\ 

\ 

\ 

► 

^V 

x,  >e>. 

^ 

*»* 

^ 

TtxW3 

^v^ 

*g* 

?£es,/' 

L 

Vfmett 

rs) 

O  I  Z  3  4  5 

Fig.  39. — Nucleation  (ions)  produced  by  a 
radiating  X-ray  bulb  (cased  in  lead  or 
not  as  stated),  at  different  distances  (D) 
from  the  glass  fog  chamber.    Table  32. 


Fig.  40. — The  same,  illustrating  table  15, 
Chapter  II. 


The  curves  I  and  II,  fig.  39,  for  the  free  bulbs  show  different  nuclea- 
tions,  compatibly  with  the  different  values  of  dp  applied,  but  are  other- 
wise alike  in  character.  They  in  no  way  suggest  the  law  of  inverse 
squares.  The  curves  III  and  IV  for  the  inclosed  bulb  are  again  similar 
in  character,  but  beyond  this  very  little  can  be  stated.  If  in  case  of 
series  II  and  III,  for  instance,  the  law 

*  (A+D)2  =  const. 

is  assumed,  the  constant  A  would  have  to  be  from  1.2  to  2.7  meters  in 
the  first  case,  and  1.5  to  2.1  meters  in  the  second,  which  is  entirely 
out  of  the  question  for  a  fog  chamber  less  than  0.5  meter  long.     If  the  law 

n  G4+D)=  const. 

is  used,  in  the  first  case  (II)  A  =0.3  to  0.1  meter;  in  case  III,  A  =  -0.2  to 
-  0.6  meter.  This  decrease  would  then  be  too  fast  in  the  first  case  and 
too  slow  in  the  second,  or  the  decrement  in  case  of  the  open  bulb  is 


DISTANCE    EFFECTS.  85 

slower  and  in  case  of  the  inclosed  bulb  (lead  box  with  window)  faster 
than  the  first  power  of  distance. 

In  fig.  40  I  have  inserted  data  incidentally  obtained  in  Chapter  II, 
table  1 5  (upper  curve) ,  together  with  data  of  the  same  kind  in  the  earlier 
reports  (lower  curve).  The  former  are  the  steepest  curves  obtained  and 
the  latter  the  least  so.  Here,  as  elsewhere,  it  is  difficult  to  conjecture 
a  reason  for  this  apparently  erratic  difference  of  behavior,  unless  it  be 
referred  to  the  facility  with  which  secondary  radiation  is  evoked,  and  to 
the  degree  in  which  the  fog  chamber  is  pervious  to  it  or  generates  it. 
Since  dn/dt  =  a-bn2  =  o,  where  a  is  the  number  of  ions  produced  per 
second,  a  must  vary  as  the  square  of  the  number  of  ions,  n,  observed. 

58.  The  same,  continued.  Small  wood  fog  chamber. — The  data  of  the 
last  paragraph  with  the  glass  fog  chamber  suggest  a  comparison  with 
the  wood  fog  chamber.  The  latter  is  much  the  more  pervious  and  in 
the  earlier  work  showed  a  much  smaller  distance  effect.  Table  33  con- 
tains eight  series  of  results.  In  series  I,  fig.  41,  the  march  is  not  unlike 
the  case  for  the  glass  chamber;  but  in  series  II  the  insignificant  differ- 
ence between  a  bulb  distance  of  50  and  100  cm.  from  the  fog  chamber 
(curves  III  and  IV)  are  similar  to  I,  and  often  betray  the  incidental 
weakening  of  the  X-ray  bulb.  In  the  series  VI  to  VIII,  change  of  the 
drop  of  pressure  (dp)  was  introduced,  but  the  inherent  difficulty  of  coping 
with  the  bulb  variations  is  seen  in  the  details  in  fig.  43. 

It  is  probable  that  the  ordinates  of  the  curves  V  to  VIII  (figs.  42  and 
43)  are  proportional  to  each  other;  but  a  discussion  is  beyond  my  present 
purpose.  The  slow  order  of  change  with  distance  should,  however,  be 
noticed. 

59.  The  same,  continued.  Large  wood  fog  chamber. — It  is  with  this 
apparatus  that  the  coronas  of  almost  the  same  aperture  were  obtained 
in  the  earlier  work,  while  the  X-ray  bulb  was  moved  from  1  to  6  meters 
from  the  fog  chamber.  Table  34  and  fig.  44,  however,  show  that  this 
result  must  have  been  due  to  other  conditions,  for  there  are  changes  of 
nucleation  here  registered  amounting  in  case  of  the  distance  specified 
(1  to  6  meters)  to  n' '111  =  145/104  at  dp  =  22\  77/41  at  dp  =  ig.  For 
greater  pressure  differences,  dp  =  25  and  29,  the  occurrence  of  terminal 
coronas  would  interfere  with  the  comparisons.  At  higher  exhaustions 
still,  the  efficiency  of  air  nuclei  would  be  gradually  restored,  so  that  the 
observed  nucleation  may  be  greater  with  the  bulb  at  6  meters  than  at 
1  meter  from  the  fog  chamber  (see  Chapter  II,  figs.  24  and '2 5).  At  "the 
very  low  exhaustion  dp  =  17  the  coronas  are  too  small  to  be  serviceable 
for  comparison. 


86 


VAPOR    NUCLEI    AND    IONS. 


ZOO 


ISO 


140 


120 


100 


80 


60 


u 

X 

■ 

FIG. 

41 

\ 

\ 

j 

N 

> 

■ 

s 

R 

■ 

h\ 

^r 

\ 

^•* 

H 

TlXlO~3 

■r-fe 

L 

D  in  cm 

\     Air, 

4(70 


3<?0 


\. 

\ 

J9&. 

<?2 

V 

nxlO'3            *■ 

•— >2>  /  7  C/77  J. 

l_ ,         > 

^^£»5 

^^; 

/00  ?O0  3<7<7  400  500  600 


60 


?0 


100         ZOO         300         400         500        600 


\ 

\ 

FIG. 

43 

T2Z7  \ 

ThxlO'3 

*\ 

^J 

L 

9  A)  c/77. 

Y 

0  100  ZOO  300  400  500 

Figs.  41,  42,  and  43. — Nucleations  (ions)  produced  by  a  radiating  X-ray  bulb  at 
different  distances  (D)  from  the  small  wood  fog  chamber.     Table  34. 

With  regard  to  the  work  of  table  34  it  should  be  stated  that  it  is 
always  customary  to  make  a  second  exhaustion  to  remove  the  water 
nuclei  left  by  the  first.  Again  but  two  distances  (1  and  6  meters)  were 
selected  to  guard  against  losses  of  efficiency  of  the  X-ray  bulb,  so  far  as 
possible.  The  exhaustion  was  made  during  the  exposure,  which  was 
always  brief.  At  the  distance  D  =  6  meters  from  the  bulb,  there  is  a 
terminal  corona  at  dp  — 22  cm.;  at  D  =  i  meter  it  appears  a  little  later 
at  0/7  =  25.  (See  Chapter  II,  figs.  24  and  25.)  In  fig.  45  the  correspond- 
ing points  are  joined  by  straight  lines,  for  convenience. 

60.  The  same,  continued.  Discussion. — Experiments  of  the  present 
kind  are  hampered  by  two  annoying  difficulties,  the  first  being  the 
variability  of  the  X-ray  bulb,  the  other  the  tendency  of  the  wooden  fog 
chambers  to  develop  slight  leaks  which  often  pass  unobserved.  True, 
the  chamber  is  tested  by  a  second  exhaustion  after  each  of  the  coronas 
measured;   but  the  unfiltered  atmosphere  entering  anywhere  is  liable  to 


DISTANCE    EFFECTS. 


87 


produce  a  disproportionate  amount  of  distortion,  because  of  the  relatively 
large  size  of  the  nuclei  contained.  Hence  it  is  of  little  value  to  attempt 
to  systematize  the  above   results  in  the   absence   of   a   well-digested 


Table  33. — Revision  of  distance  effect. 

X  45  cm. 


X-rays.    Small  wooden  fog  chamber 
dp  =21.7  cm. 


5Xi 


X-rays  off 
X-rays  on 


II. 

X-raysoff 
X-rays  on 


III. 

X-rays  on 


Bulb 
weaker 
IV. 
X-rays  on 


V. 

X-rays  on 


VI. 

X-raysoff 
X-rays  on 


D. 


cm. 

2ioo 
600 
600 
600 
400 
400 
200 
200 
100 
100 
100 


100 

50 

50 

100 

100 

100 

400 
400 
600 
600 
600 
400 
400 

200 
400 
600 
600 
600 

400 

200 

100 

50 

25 


»5 

2,S 


2.8 


9.2 

7-i 
7.2 
35-6 
6.2 
6.1 

6-3 
6.2 


6.4 
7-4 
7-9 
7-9 
8-5 

4.o 
9.6 
9.0 


Corona 


wrg 


w  y' 
w  r 
g'B 

g'BP 


w  r  g 
wrg 
wrg 
wrg 
wrg 

w  r 
w  y 
w  y 
cor 


g'BP 


gBP 
g'BP 

wrg 


w  b  r 
w  r 
w  p 
w  p 

wp'g 


wrg 
wp 


n  xio-8 


7 
180 

47 
55 
58 
67 
65 
100 

9i 
112 
118 
112 

7 
180 
180 
180 
180 
180 

180 
103 
106 

55 
7i 
68 

74 
7i 

120 

85 
26 

53 
61 

77 
112 
144 
144 
156 

o 

TOO 

175 


D. 

5 

Corona. 

VI. 

cm. 

X-rays  on 

25 

9.0 

wp 

100 

8 

0 

wB  P 

100 

7 

8 

wB  P 

300 

7 

3 

w  r  0  g 

300 

7 

3 

wr 0  g 

600 

5 

4 

wrg 

600 

5 

2 

nXio- 


175 
120 
120 
100 
100 
50 
45 


High  dp  =  27. 5. 


VII 

X-raysoff 
X-rays  on 


VIII 


54-6 

600 

5 

8 

400 

6 

7 

w  y' 

200 

9 

5 

wrg 

100 

11 

0 

wyog' 

50 

11 

5 

wyg 

10 

gyo? 

10 

5 

9 

w  y' 

7 

6 

wr 

100 

7 

2 

wr 

10 

7 

4 

g'BP 

IOO 

7 

5 

wyg' 

600 

84 

1 

cor 

\ 

7 

cor 

•5 

0 

cor 

400 

85 

0 

cor 

200 

7 

0 

wrg 

IOO 

7 

6 

wyg 

20 

7 

6 

wyg 

IOO 

7 

3 

wrg 

200 

5 

9 

wrg 

300 

5 

6 

cor 

400 

tt5 

5 

500 

°5 

1 

600 

84 

2 

600 

64 

3 

IOO 

86 

4 

wrg 

6. 
70 
105 
225 
280 
350 
420 

59 

93 

87 

109 

84 
18 

3i 
35 
35 
93 
98 
98 
82 

59 
50 
48 
38 
21 
23 
76 


'=25.3,  »=5-7. 


*0P=  25.3.  »=  5-7.  *Freshbulb.  3  Battery  current  weak. 

4  Second  exhaustion  without  rays  made  (after  the  first)  to  remove  water  nuclei. 

•#£=28.1,    «=48,  n=s7,ooo;    dP=  29.7,  »=  5.2,  n=  55,000;    §p=*  31.9,  #=5.6,  n=  71,000. 

6  Coronas  large  on  the  near  end  and  small  on  the  far  end  of  fog  chamber.     Subsidence  oblique. 


VAPOR    NUCLEI    AND    IONS. 


Table 

34. — Revision  of  distance  effects.     Large 
cm.     Exhaustion  during 

wood  fog  chamber 
exposure. 

.     20X12X55 

dp 

=  19.0  cm. 

ty-17.1. 

D. 

s. 

Corona. 

n  xicrs. 

D. 

s. 

Corona. 

n  X  10-3. 

X-rays  off 

X-rays  on 

IX. 

600 
600 
100 
600 
600 
600 

1 .2 
5-3 
4-5 
6.6 

5-2 

4.0 

just seen 

1.2 

43 
26 

77 
4i 
39 
18 

XII. 

600 
100 

1 .0 

2.8 

1 .0 

5-3 

dp  =  24.8* 

XIII. 

100 

Mr 
100 
M- 

100 
600 
100 

9-5 

27.6 

10. 0 

29.4 

^0 

6.2 
10 

wrog' 

wrog 

wrog 

wrg 

wrog 

236 
254 

265 
no 
265 

dp 

=  21.8  cm. 

X. 

600 
100 
100 
600 
600 

5-6 
8.7 
8.8 
6.6 
6-5 

w  p 
w  p 
w  r 
w  y 

56 
145 
145 
103 
103 

dp 

=  25.1  cm. 

XI. 

600 
100 
600 

6.5 
9-5 
7.0 

wog 

wrog' 
w  y 

112 
236 
119 

♦Terminal  corona;  same  for  7  and  9  cells. 


theory  of  the  phenomena;  but  the  equations  n  =  n0/(A  +D)2  and  n  = 
n0/(A+D),  where  A  is  constant  and  D  the  distance  between  bulb  and 
fog  chamber,  may  be  adduced  to  accentuate  the  order  of  values  observed. 
This  has  been  done  in  case  of  table  32,  showing  that  for  the  non-incased 
bulb  even  the  inverse  first  power  of  D  varies  more  rapidly  than  the 
observed  phenomenon.  To  a  much  greater  extent  is  this  true  for  the 
wood  fog  chambers.  The  phenomenon  itself  is  clearly  a  case  of  super- 
position of  primary  and  secondary  radiation.  The  latter,  moreover,  is 
furnished  not  only  by  the  environment  of  the  X-ray  bulb,  as  shown  in 
fig-  39  by  surrounding  the  bulb  with  a  windowed  lead  case,  but  also  by 
the  immediate  environment  of  the  fog  chamber.  The  small  distance 
variation  encountered  would  then  seem  to  be  explained  by  supposing 
that  relatively  much  secondary  radiation  is  released  by  relatively  weak 
primary  radiation,  as  compared  with  a  case  of  strong  primary  radiation. 
Under  all  circumstances  the  total  effect  is  an  integral  to  be  extended 
over  the  whole  surface  and  possibly  the  interior  of  the  room.  Finally, 
one  should  recall  that  the  rate  at  which  ions  are  produced  by  the  radi- 
ation must  vary  as  the  square  of  the  number  observed. 


DISTANCE    EFFECTS. 


89 


240 


220 


200 


180 


140 


120 


O  (00  200  300         400         500         600 

Fig.  44. — Nucleations  (ions)  produced  by  a  radi- 
ating X-ray  bulb  at  different  distances  (D) 
from  the  large  wood  fog  chamber.     Table  34. 

61 .  Distance  effect  and  absorption.  Radium. — A  few  experiments  were 
made  incidentally  with  impure  radium  (10  mg.  1 0,000  X,  sealed  in 
aluminum),  using  the  method  of  depression  of  the  terminal  asymptote. 
In  table  36,  for  instance,  results  are  recorded  on  the  absorption  of  the 
y-rays  in  lead.  Fig.  45  shows  the  results  in  relation  to  the  nucleation  of 
dust-free  air,  the  efficient  nucleation  of  which  is  more  and  more  reduced 
as  the  intensity  of  the  radiation  increases  with  the  diminishing  thickness 
of  the  absorbing  lead  envelope. 

After  nearly  1.6  cm.  of  lead  have  been  penetrated,  the  distance  of  the 
curve  from  the  asymptotic  air  line  is  still  marked.  Results  of  this  kind 
should  furnish  valuable  data  for  testing  any  theory  on  the  distribution 
of  precipitated  moisture  on  graded  nuclei  under  any  definite  conditions. 

Table  36  gives  an  incidental  series  of  distance  effects  worked  out  by 
the  same  methods.    As  exhibited  in  fig.  46,  the  first  series  reaches  the 


9o 


VAPOR    NUCLEI    AND    IONS. 


too 


cms.  of 


FIG. 


45 


Oust  -fr  ?e  air 


.8 


Fig.  45. — Depression  of  efficient  nucleation  (n)  of  dust-free  air,  ionized  by  gamma-rays 
of  radium  penetrating  through  different  thicknesses  of  lead.     Table  35. 


Table  35. — Absorption  of 
lead.  7-rays  of  radium 
10,000  X.  D  =  ioo  cm.; 
dp  =31  cm. 


high  asymptote  for  dust-free  air  practically  at  a  distance  of  D  =  150  cm. 
In  the  second  series  the  asymptote  is  lower,  due  to  details  in  the  ad- 
justment in  the  apparatus,  and  reached  later,  i.  e.t  at  a  distance  of  D  = 
180  cm.  between  the  radium  and  the  fog  chamber.    This  curve  has  been 

worked  out  completely  for  D  =  o  cm.,  and 
shows  the  very  interesting  feature  of  a  well- 
developed  minimum.  In  other  words,  as  the 
radium  is  removed  from  the  fog  chamber,  the 
ions  which  at  first  predominate  and  capture 
all  of  the  moisture  decrease  more  and  more 
in  number,  until  the  conditions  are  ripe  for 
the  simultaneous  condensation  of  moisture 
on  the  colloidal  nuclei  of  dust-free  air.  In 
proportion  as  the  radium  is  further  removed, 
the  latter  predominates,  fully  so  when  the 
asymptote  is  reached. 

The  corresponding  results  when  the  radium 
tube  is  inclosed  in  a  thick  lead  pipe  (walls 
5  mm.,  length  60  cm.)  shows  a  much  sharper 
minimum,  occurring  at  lower  exhaustions.  Such  irregularities  as  are 
apparent  here  may  be  referred  to  the  unequal  distribution  of  radiation 
within  the  fog  chamber  discussed  in  Chapter  I,  sections  4  et  seq.  All  of 
these  curves  have  a  similar  bearing  on  the  question  of  the  distribution 
of  the  precipitate  of  graded  nuclei. 


Thickness 

n  Xio-3. 

t 

s. 

00 

7.2 

131 

i-54 

6.0 

85 

6-5 

103 

6-5 

103 

0.40 

6.0 

85 

5-9 

82 

.0 

4.9 

49 

4.8 

46 

00 

7.0 

128 

DISTANCE    EFFECTS. 


91 


Table  36. — Distance  effect  and  absorption  of  radium  rays.     D  measured  from  side. 
dp  =  31.     November  2.     Lead  pipe  0.5  cm.  thick,  60  cm.  long 


D. 

s. 

wXio"5. 

D. 

s. 

n  X  io~s. 

II 

cm. 
180 
150 
100 

50 

25 

10 

2.2 

0 
350 
300 
250 

6.2 
5-9 
4-7 
3-7 

3-7 
4-7 

4.8 
5.6 
6.7 
6.8 
6.2 

90 
82 
42 
21 
21 
42 

46 

70 

in 

116 

90 

III. 

In  lead  pipe . . 

On  top 

At    00 

cm. 

145 

100 

50 

25 

10 

1 

5.6 
4-7 
4-3 
4-i 
4.0 

49 
7.2 

70 
42 
32 
27 
24 
49 
135 

Above  fog 

chamber . .  . 
On  glass 

Radium 

at  00    0 

120 

100 

FIG. 

46 

1/ 

— n 

60 
40 
20 

/ '^m 

L 

/ 

-^ 

V 

/ 

\\ 

s* 

^-O— 

& 

^ 

nxio'3 

IT 
D  in  en 

5. 

60 


too 


leo 


zoo 


Fig.  46. — Minima  of  efficient  nucleations  observed  at  high  exhaustions  with   radium  at 
different  distances  (D)  from  the  fog  chamber.     Table  36. 

62.  Falling  to  pieces  of  ions  in  the  lapse  of  time. — Miss  L.  B.  Joslin 
contributes  the  following  interesting  observations  obtained  by  the 
method  of  depression  of  the  terminal  asymptote. 

The  data  summarized  in  table  37  and  fig.  47  were  obtained  by  acting, 
in  the  manner  stated,  on  the  dust-free  moist  air  contained  within  a  glass 
fog  chamber,  with  a  sample  of  weak  radium  (io,oooX,  10  mg.),  sealed 
in  an  aluminum  tube.  This  was  placed  on  the  outside  of  the  chamber 
in  contact  with  its  walls  (0.2  to  0.3  cm.  thick),  and  was  then  removed 


92 


VAPOR    NUCLEI    AND    IONS. 


suddenly  at  given  intervals  before  exhaustion.  Only  very  penetrating 
primary  rays  (/?  and  y)  are  therefore  in  question.  The  curves  show  the 
number  of  efficient  nuclei  in  thousands  per  cubic  centimeter,  observed 
after  the  lapses  of  time  shown  by  the  abscissas,  and  it  is  supposed  that 
the  nuclei  are  reproduced  faster  than  they  can  be  removed  by  the  ex- 
haustion. In  the  upper  curve  the  pressure  differences  applied  (^  =  31) 
are  much  above  the  fog  limit  of  dust-free  air,  which  is  below  d£0  =  24  for 
the  given  apparatus.  In  the  lower  curve  the  pressure  differences  are 
nearly  at  the  fog  limit  of  dust-free  air,  while  the  other  curve  (dp  =  28) 
applies  for  intermediate  conditions.  The  effect  of  the  radiation  is  there- 
fore, virtually  at  least,  a  coagulation  (to  use  a  figurative  expression)  of 

Table    37. — Falling  to    pieces    of    ions    produced    by    radium.     Everything    ready; 
cocks  closed  before  removing  radium. 


Date. 


Oct. 


/.* 


Cor. 


MX  IO" 


h-31 


sec. 

CO 

7-4 

w'  obg 

O 

5 

8 

cor 

15 

4 

O 

cor 

30 

5 

0 

cor 

60 

5 

9 

coyg 

90 

6 

7 

wog 

120 

7 

2 

wog 

180 

7 

5 

wog 

^  =  24.5  cm. 


Oct.  24 

0 

6-3 

5 

5 

1 

wrg 

10 

4 

7 

wrg 

15 

3 

7 

20 

3 

6 

25 

3 

2 

30 

2 

3 

5 

4 

8 

wog 

10 

4 

2 

wrg 

12.5 

3 

9 

wrg 

140 

76 
24 
51 

82 

III 

134 
145 


79 
45 
36 
18 
16 
11 
3- 
45 
29 
23 


Date. 


/.* 


Cor. 


MX  IO" 


=  28  cm. 


Oct.  25 


sec. 

o 

15 

30 

45 

60 

120 

180 

00 

00 


5-8 
3-8 
3-5 
3-3 
34 
4-7 
4.6 
4.6 
4.8 


wrg 
wog 


72 
21 
16 
13 
14 
40 

37 
37 
43 


Oct .  2  7  Repeated .    Decay  of  ions  at  dp  —  24 


Radium  on . . . 
Radium  at  00  . 
Radium  on .  .  . 


60 

2 

i-3 

30 

3-3 

t3Q 

3-2 

15 

4.2 

10 

4-7 

0 

6.2 

2.5 

1.6 
12. 1 
11. 4 

25 
36 

77 


Fog  limit  of  air.       Radium  off. 


dp 


23.6 
22.6 


*  Seconds  elapsed  after  removal  of  radium. 

t  First  coronas  dense  but  fall  out  rapidly,  leaving  fainter  and  smaller  coronas  behind. 


DECAY    OP    IONS. 


93 


the  colloidal  nuclei  of  dust-free  air  into  the  aggregates  much  larger  in 
size  representing  the  ions.  Hence  in  the  presence  of  radium  under  the 
given  conditions  the  number  of  efficient  nuclei  decreases  either  because 
the  ions  from  their  size  capture  all  the  available  moisture  more  and  more 
fully,  or  because  the  colloidal  nuclei  have  actually  been  aggregated  into 
fewer  but  larger  systems,  which  will  in  turn  fall  apart  in  the  absence  of 
radium. 


120 


100 


zoo 


Fig.  47. — Efficient  nucleation  observed  within  the  fog  chamber  at  different  times  after 
exposure  to  radium  applied  outside  at  different  exhaustions  (dp).     Table  37. 


It  follows  from  what  has  been  stated  that  above  the  fog  limit  of  dust- 
free  air  the  number  of  efficient  nuclei  must  increase  with  the  removal 
of  radium  at  a  rate  which  corresponds  to  the  falling  to  pieces  of  the  ions. 
The  peculiar  feature  of  the  results  here  in  question  is  the  manner  in  which 
the  efficient  nucleation  decays  from  the  coarser  ionized  to  the  finer 
non-ionized  colloidal  stages,  when  the  pressure  difference  is  decidedly 
above  the  fog  limit  of  air,  so  that  the  latter  may  be  recognized.  The 
curves  invariably  pass  through  a  minimum  when  the  time  after  the 
removal  of  the  radium,  i.e.,  the  interval  of  decay,  increases  indefinitely. 

This  minimum,  moreover,  is  very  sharp,  almost  cusp-like,  as  if  one  law 
were  passing  abruptly  into  another.  Thus  below  the  minimum  (/  =  i3 
sec,  about)  the  curve  for  dp  =  31  nearly  coincides  with  the  curve  for 
dp  =  24,  which  is  practically  independent  of  the  colloidal  nuclei  of  air. 
The  decay  may  be  computed  to  be  of  the  order  of  that  of  ions.  After  a 
lapse  of  13  seconds  the  effect  of  colloidal  nuclei  is  marked  for  dp  =  31; 
and  even  after  a  lapse  of  60  seconds,  when  the  ions  (lower  curve)  have 


94  VAPOR    NUCLEI    AND    IONS. 

vanished  to  a  few  hundred,  the  upper  curve  is  only  half  way  on  its  march 
toward  the  asymptote.  This  shows  the  remarkable  sensitiveness  of  the 
method  as  a  test  for  the  presence  of  ions  or  of  any  nuclei  larger  than  the 
colloidal  sizes.  Moreover,  measurement  of  the  large  coronas  is  relatively 
easy.  Finally,  the  curve  dp  =  31,  if  prolonged  backwards,  would  seem  to 
start  nearly  from  the  origin ;  in  such  a  case  one  would  have  to  picture  to 
oneself  a  single  particle  breaking  to  pieces,  in  the  absence  of  radiation, 
into  fragments  of  continually  decreasing  size,  until  the  debris  ultimately 
numbers  150,000  colloidal  nuclei. 

The  intermediate  curve  (dp  =  28)  also  coalesces*  approximately  with 
the  other  curves  for  lapses  of  time  less  than  t  =  1 3  seconds.  It  has  its 
own  minimum,  however,  and  from  the  lower  pressure  difference,  neces- 
sarily its  own  asymptote  at  n  —  40,000,  since  only  the  coarser  order 
of  air  nuclei  fall  within  the  given  limits  of  condensation  in  the  apparatus 
used.  For  the  same  reason  the  minimum  is  lower  and  later,  seeing  that 
the  ions  are  present  throughout  in  relatively  greater  numbers  as  com- 
pared with  the  efficient  colloidal  nuclei,  than  was  the  case  at  dp  =  31. 

The  curves  as  a  whole  have  so  close  a  resemblance  to  the  data  inves- 
tigated in  section  61  for  the  effect  of  radium  at  different  distances 
from  the  fog  chamber  that  the  same  cause  must  underlie  both  series  of 
observations.  In  the  former  case  (distance  effects)  any  given  intensity 
of  ionization  between  the  maximum  and  the  vanishing  values  may  be 
maintained  indefinitely  by  properly  placing  the  radium  tube;  in  the 
latter  case  (decay)  all  stages  are  passed  through  in  2  or  3  minutes. 
Beginning  with  dust-free  non-energized  air,  the  number  of  efficient 
nuclei  decreases  as  the  number  of  ions  increases  (for  either  or  possibly 
both  of  the  reasons  already  given)  until  the  condensation  takes  place 
wholly  on  ions.  For  greater  intensities  of  ionization  the  number  of 
ions  must  increase  further,  and  hence  the  efficient  nucleation  rises  again 
while  the  curve  passes  through  a  minimum. 

I ,  The  curves  enable  us  to  make  certain  interesting  comparisons,  inas- 
much as  the  same  nucleation  results  from  radium  decaying  for  a  stated 
length  of  time,  as  results  from  the  action  of  radium  at  a  certain  distance 
from  the  line  of  sight.  From  the  importance  of  secondary  radiation 
in  connection  with  these  observations,  such  comparisons  are  probably 
not  simple.  The  essential  feature  is  the  passage  of  the  nucleation 
through  the  same  stages  of  variation,  whether  of  size  or  of  number,  in 
both  cases  no  matter  how  the  given  successive  intensities  of  ionization 
may  be  produced,  or  whether  they  come  from  within  or  without. 

*  Considered  relatively  to  the  wide  divergence  after  ^  =  13  sec.  is  passed.  The  coales- 
cence need  not  be  perfect.     Small  coronas  fall  out  too  rapidly  for  close  measurement. 


DECAY    OF    IONS. 


95 


63.  Decay  curve. — Assuming  that  the  rate  of  decay  in  the  lapse  of 
time  (t)  is  as  the  square  of  the  number,  or  that  i/n  —  i/w'  =  6  (/-/') 
where  6  is  constant,  a  few  incidental  attempts  were  made  to  compute  6. 

Table  38  and  fig.  48  contain  an  example  of  such  results,  obtained 
by  exhausting  the  fog  chamber  at  a  stated  time  after  the  removal  of 
radium.  The  drop  in  pressure  is  below  the  coronal  fog  limit  of  air  and 
all  precipitation  takes  place  on  ions. 


60 


20 


nxl0~3i 
♦ 

N. 

FIG. 

48 

t 

*-5ec. 

*" + .6. 

1 

50 


Fig.  48. — Decay  of  ionized  nuclei  (n  per  cubic  centimeter)  produced  by 
radium  in  dust-free  air,  in  the  lapse  of  seconds.     Table  38. 


Table  38. — Decay  curve  at 
dp  =23.    Radium  on  top. 


For  the  first  five  seconds  6  =  0.0019,  for 
the  first  fifteen  seconds  6  =  0.0022,  etc., 
the  values  obtained  ranging  from  0.002  to 
0.003.  This  is  larger  than  the  electrical 
datum  0.0014.  Decay  is  more  rapid  than 
the  equation  warrants.  Initial  coronas  are 
too  large,  final  coronas  too  small,  in  spite 
of  the  presence  of  air  nuclei,  the  number 
of  which  should  be  deducted  at  least  in 
part.  Other  experiments  show  similar  co- 
efficients. Thus  the  low  curve  of  Miss  Jos- 
lin  would  conform  to  6=0.0023.  Natu- 
rally the  present  method  for  6  is  much 
inferior  to  the  electrical  method,  even  if 
the  two  coefficients  are  identical ;  but  the  6  here  is  obtained  under  pos- 
sible complications  with  the  larger  gradations  of  the  colloidal  nuclei  of 
dust-free  air,  though  these  are  probably  inefficient. 

If  the  values  of  i/n  be  inserted,  the  curves  should  be  linear,  since  i/w 
=  i/w0  +  6/,  where  t  is  the  time  dated  since  the  occurrence  of  n0.  The 
line  passing  through  the  observations  at  5,  30,  50  seconds  is  best  adapted 
to  represent  the  results,  and  compatibly  therewith  6 -=0.0024  («  in 
thousands  of  nuclei  per  cubic  centimeter)  may  be  roughly  assumed. 
These  computed  values  of  n  are  given  in  table  38  and  shown  in  the  chart 
(fig.  48).     They  are  too  low  initially  and  too  high  finally,  even  if  the  air 


t. 

s. 

n  x  io-s. 

n  x  io-s. 
b  =.0024 

sec. 

0 

5-9 

67 

675 

5 

50 

4i 

37-3 

10 

4.6 

32 

25.8 

15 

4.0 

21 

19.7 

20 

3-5 

15 

159 

30 

3-3 

11. 6 

"•5 

50 

2.9 

7-4 

7-4 

120 

1-7 

i-9 

3-3 

00 

1.0 

1. 1 

96  VAPOR    NUCLEI    AND    IONS. 

value  is  quite  ignored;  but  the  constant  probably  reproduces  the  true 
conditions  better  than  the  observation,  remembering  that  the  initial 
corona  (t  =  o)  is  not  quite  invariable. 

A  very  important  consequence  may  be  deduced  from  these  results. 
The  equations  specified  may  be  written 


(?-)=»• 


Hence  if  the  ratio  of  nucleations  or  of  ions  is  known  (for  instance  by  the 
method  of  geometric  sequences),  n0/n  is  given,  and  the  absolute  value 
of  n  may  be  computed  if  6  is  known.  Now,  if  6,  for  the  case  of  ions, 
may  be  taken  as  identical  with  the  value  found  in  electrical  experiments, 
where  6  =  0.0014,  roughly  and  relative  to  ionization  in  thousands,  bn0  = 
0.0014  n\  where  n\  is  the  true  nucleation.  Thus  in  table  39,6  =  0.0024, 
n0  =  67,500;  therefore  w'0=  (0.0024/0.0014)  nQ  or  115,000  nuclei  per  cubic 
centimeter.  Quite  generally,  if  n0/n  and  b  are  determined  from  purely 
coronal  measurements  6/0.0014  is  the  reduction  factor  for  all  the  rela- 
tive nucleations  to  absolute  values. 

Another  very  important  consequence  may  be  drawn.  If  the  coeffi- 
cient is  known  from  direct  experiments,  it  will  then  be  possible  to 
standardize  the  residual  curve  (depressed  asymptote)  leading  to  the 
terminal  corona.  Thus  if  6  =  0.0024  is  roughly  assumed,  as  an  example 
derived  from  the  data  at  dp  =  24  cm.  (table  37  and  fig.  47),  the  value 
of  the  ordinates  of  the  curve  for  dp  =  31  would  then  be  given  by  table 
39  and  fig.  49. 

Moreover,  in  any  such  curve,  while  the  ordinates  denote  the  computed 
number  of  ions,  the  abscissas  denote  the  observed  number  of  efficient 
colloidal  nuclei  and  ions  in  the  course  of  time,  largely  the  former.  Hence 
the  curve  gives  an  indication  of  the  distribution  of  the  precipitated 
water  on  the  two  groups  of  nuclei,  different  in  size  and  present  in  different 
proportions,  for  the  given  supersaturation.  Experiments  of  this  kind  are 
of  the  highest  importance  and  the  present  cursory  treatment  is  admitted 
provisionally,  in  view  of  a  projected  restandardization  of  the  coronas  of 
cloudy  condensation,  which  the  variety  of  results  since  obtained  has 
made  necessary.  The  curve  for  6  =  0.0024  is  shown  in  fig.  48;  the  two 
curves*  i  and  n+i,  i  and  w,  in  fig.  50.  The  initial  descent  of  the  graph 
for  i  and  n  is  clearly  steeper  than  would  correspond  to  any  exponential 
or  hyperbola,  and  an  equation  of  the  form 

i  (n+A)B  =  C 
is  at  least  needed  to  express  the  data.     The  computation  of  the  constants 

*  Where  i  denotes  the  number  of  ions,  n  the  number  of  nuclei  per  cubic  centimeter. 


DECAY    OF    IONS. 


97 


would  not  be  of  any  value.  The  table  and  chart  show  clearly  enough 
how  rapid  a  reduction  of  efficient  nuclei  is  produced  by  the  presence  of 
but  a  few  thousand  ions.  The  results  would  have  been  much  more 
striking  if  a  more  efficient  form  of  apparatus  had  been  used,  since  for 
dp  =  31  cm.  it  is  customary  to  obtain  four  or  more  times  as  many  col- 
loidal nuclei  in  the  absence  of  ions. 


Table  39. — Graduation  of  high  pressure  curve. 
i/rio  =0.0133  =  0. 


6=0.002;  n0  =75X10-'; 


i/w0  =  A  =0.0133; 

b  =0.0024. 

t. 

n  Xio  3 

atd/>«3i.   a. 

hbt. 

n  X  io-3. 

\  (n+i)~i  }   X 
io-3  =  n  X  io_s. 

sec. 

10 

*29        0 

0373 

f26.8 

2 

20 

32 

0613 

16.3 

16 

30 

5i 

0853 

11. 7 

39 

40 

62 

1093 

9.2 

53 

50 

74 

1333 

7-5 

67 

60 

85 

1573 

6.4 

79 

80 

105 

2053 

4-9 

100 

100 

120 

2533 

4.0 

116 

120 

135 

3013 

33 

132 

140 

140 

3493 

2.9 

137 

160 

3973 

2.5 

180 
5 

145 

4453 

2.2 

143 

.0253s 

39-5 

15 

.0493s 

20.3 

*(i+n)Xio-». 


t»Xio-». 


O  20  40 

Fig.  49. — Decay  of  ions  (f  per  cubic  centimeter)  in  dust-free  air,  evidenced  by 
increase  of  efficient  colloidal  nucleation  (n  per  cubic  centimeter).     Table  39. 

64.  The  same,  continued. — In  conclusion  I  may  state  that  a  number 
of  experiments  were  made  to  test  the  rate  at  which  the  ions  are  gener- 
ated. If  a  is  the  number  of  ions  produced  by  the  rays  per  cubic  centi- 
meter per  second  and  b  the  coefficient  of  decay , 

dn/dt=a  —  bn2 


98  VAPOR    NUCLEI    AND    IONS. 

This  may  be  written 


1       Cd  (dn/dt) 
/fcj  (dn/dtWa^ 


t  = =  I  — : — : — -  —  -f  C 

2VbJ  (dn/dtWa- dn/dt 


from  which,  after  integration, 


-2^/ab't+c    N-y/a/b 

if 

n  —  n1      .   —2bnxt 

—Ac 

nXfit 


where  A  is  a  constant  and  w1  =  >/a/6, 

i+Ae-2bnJ 
xi-Az~2bnJ 


n  =  n 


If  t  =  00  ,  n  =  nt,  a  =  bn2,  which  is  otherwise  evident.  The  coefficient 
a  is  here  taken  as  an  absolute  constant  independent  of  n.  In  the  pre- 
ceding paragraph  it  was  roughly  assumed  that  6  =  0.002  if  n  is  reckoned 
in  thousands  per  cubic  centimeter.  Hence  a  =  0.000002  X  n2.  Thus 
if  w  =  io3,  a  =  2  per  cubic  centimeter  per  second;  if  w  =  io6,  a  =  2  X  io6, 
etc.  Experiments  were  tried  with  the  radium  tube  on  a  pendulum 
swinging  above  the  fog  chamber;  also  with  the  tube  on  an  inclined  plane 
moving  rapidly  across  the  chamber.  But  in  both  cases  the  results, 
which  essentially  require  the  opening  of  the  stopcock  of  the  fog  chamber, 
are  too  involved  to  have  any  critical  value,  and  they  are  therefore  dis- 
carded here. 

65.  Condensation  phenomena  of  the  inclosed  steam  jet.  Methods 
and  results. — Some  time  ago  (Bulletin  No.  12,  U.  S.  Weather  Bureau, 
1893),  I  obtained  a  series  of  results  (shown  for  example  in  fig.  52)  from 
observations  of  the  behavior  of  the  steam  jet  inclosed  in  a  wide  tube 
of  thin  sheet  metal.  The  jet  shown  at  /  in  fig.  50  plays  into  the  tube 
AkA,  about  2  inches  wide  and  2  or  more  feet  long,  the  steam  escaping 
at  B.  Sky-light  L,  from  a  mirror  M,  enters  the  tube  axially,  through 
a  window  a,  and  is  observed  through  an  opposite  window,  g.  Room  air 
enters  at  C,  to  cool  the  steam,  and  the  temperature  of  the  inflowing  air 
is  taken,  as  well  as  the  pressure  under  which  the  steam  escapes.  Fig.  51 
shows  two  such  tubes  arranged  for  differential  work.  These  data  are 
used  in  the  construction  of  fig.  52,  where  air  temperatures  in  degrees 
centigrade  are  horizontal  and  steam  pressures  in  pounds  vertical. 


STEAM    JET.  99 

It  will  be  seen  that  for  each  temperature  of  the  inflowing  air  there 
is  a  definite  steam  pressure  at  which  the  field  of  the  tube  just  becomes 
opaque,  and  condensation  within  the  jet,  therefore,  begins  to  be  tumul- 
tuous. The  edge  of  the  opaque  field  is  sharply  marked,  and  above  15  it 
is  possible  to  pass  through  it  in  a  march  of  continually  increasing  steam 
pressures;  for  the  opaque  field  vanishes  with  a  kind  of  cusp,  dependent 
for  its  position,  naturally,  on  the  apparatus  used. 

What  the  figure  imperfectly  suggests,  however,  is  the  occurrence  of 
similar  loci  of  axial  color,  which  run  parallel  to  the  edge  of  the  opaque 
zone,  on  the  clear  side  of  it.  The  colors  follow  the  spectrum  series 
reversed,  v,  b,  g,  y,  o,  r,  growing  continually  fainter  and  vanishing  into 
daylight. 

The  field  becomes  at  once  opaque  if  a  strong  nucleator  like  phosphorus 
is  placed  near  C,  fig.  50;  or  any  color  may  be  obtained  in  this  way  by 
carefully  regulating  the  additions  of  nuclei,  as  shown  elsewhere.  Mere 
smokes,  like  salammoniac,  are  ineffective;  in  fact  the  field  made  opaque 
by  phosphorus  may  be  cleared  by  such  smoke,  added  in  reasonable 
quantity. 

Ordinary  non-filtered  air  is  practically  ineffective. — This  touches  the 
first  point  to  be  made.  I  have  shown  elsewhere  that  the  fog  chamber 
and  the  steam  jet  mutually  supplement  each  other;  the  former  respond- 
ing measurably  to  nuclei  reckoned  in  thousands  per  cubic  centimeter, 
the  latter  to  nuclei  reckoned  in  millions  per  cubic  centimeter,  to  speak 
roughly.  In  other  words,  the  whole  sequence  of  coronas,  of  which  there 
are  many  periods  visible  in  an  apparatus  of  reasonable  size,  has  been 
passed  through  when  the  occurrence  of  axial  color  begins,  the  latter  end 
with  particles  so  fine  as  to  be  optically  ineffective. 

It  is  for  this  reason  that  ordinary  non-filtered  air,  which  produces  such 
remarkable  effects  in  the  fog  chamber,  is  almost  without  effect  on  the 
steam  jet.  A  faint  scarcely  discernible  pink  tinge  is  all  that  is  seen, 
and  it  is  therefore  possible  to  omit  the  filtration  of  air  altogether.  The 
use  of  dust-free  air  will  not  change  the  conditions,  which  lie  wholly 
below  the  scope  of  the  steam  jet.  This  is  even  the  case  when  the  air 
is  artificially  dusted  by  less  powerful  nucleators  like  weak  X-rays  or 
weak  radium,  the  additions  being  as  a  rule  relatively  insignificant. 

As  the  increase  of  steam  pressure  can  only  increase  the  supersatu- 
ration,  it  follows  that  the  tumultuous  precipitation  of  the  steam  jet 
characterizing  the  opaque  zone  must  take  place  on  the  nuclei  of  dust-free 
air,  for  at  this  stage  of  the  phenomenon  the  corona-producing  dusts 
are  ineffective. 

Much  attention  has  been  given  by  Professor  Wood  in  this  country, 
and  by  others  abroad,  to  the  occurrence  of  optical  resonance  in  con- 


IOO 


VAPOR    NUCLEI    AND    IONS. 


©  © 


m 


m 


n 

[1 

11 

\\ 

M 

M' 

Fig.  si- 
Fig.  50. — Section  of  inclosed  steam  jet  and  tube. 
Fig.  51. — Binocular  inclosed  steam  jet. 

Fig.  52. — Chart  showing  margin  of  opaque  zone  for  different  steam  pressures  (pounds 
per  square  inch)  and  temperature  of  inflowing  air. 

nection  with  similar  color  effects.  But  the  case  of  the  steam  jet  may 
be  duplicated,  in  different  ways,  by  the  vapors  of  typical  non-ionizing 
liquids,  like  gasoline,  benzol,  carbon  bisulphide,  etc.,  with  even  more 
saturated  axial  colors  than  are  observable  in  steam.  Electrical  resonance 
can  not,  therefore,  be  effective  here,  where  the  fog  globules  are  dielectric. 
The  particles,  moreover,  are  too  large  to  fall  within  the  lines  of  such 
an  explanation. 

Returning  to  the  diagram  (fig.  52),  it  will  be  seen  that  at  a  temperature 
of  about  400  there  is  no  observable  condensation;  in  other  words,  the 
steam  passes  through  the  tube  like  a  gas,  leaving  the  field  quite  clear. 
At  400,  therefore,  the  supersaturation  at  which  condensation  begins  to 
take  place  on  the  nuclei  of  dust-free  air  is  just  reached;  below  it,  at  the 
given  pressure,  the  supersaturation  is  in  excess,  and  steam  pressure 


STEAM    JET. 


IOI 


must  be  relieved  to  reduce  the  excess  before  the  field  clears  again,  in 
greater  measure  as  the  temperature  is  lower,  until  at  90  steam  issuing 
at  ordinary  pressure  (without  appreciable  pressure  above  one  atmos- 
phere) condenses  spontaneously. 

The  increments  of  supersaturation  below  400  are  in  fact  considerable. 
Thus,  if  the  saturation  at  400  be  taken  as  the  standard,  these  excesses 
would  be  roughly  as  shown  in  table  40. 


Table  40. — Estimated  supersaturations. 


Temperature. . . 
Supersaturation 
Relation 


400 

35° 

30° 

25° 

20° 

15° 

IO° 

0 

12 

21 

28 

34 

3» 

42 

I 

1.3 

17 

2.2 

2.9 

3-9 

5-5 

io-9g/cm3. 


These  values  are  to  be  added  to  whatever  supersaturation  preexists 
at  400,  seeing  that  the  escaping  steam  is  always  suddenly  cooled  down 
from  a  temperature  much  above  ioo°.  In  fact,  the  following  data 
(table  41)  may  be  adduced  from  the  diagram,  if  tt  be  the  temperature  of 
the  steam  before,  t2  the  temperature  after,  pt  and  p2  the  densities  of 
the  steam. 

Table  41. — Estimated  supersaturations. 


h 

Po 

ft 

Pi 

5  =Px/P2 


40° 

35° 

30° 

25° 

20° 

15° 

IO° 

50.9 

39-3 

30.1 

22.8 

17.2 

12.8 

9-3 

112° 

112° 

112° 

112° 

111° 

1090 

'050 

894 

894 

894 

894 

865 

811 

7i5 

17.6 

22.  7 

29.8 

39-2 

50.3 

63-3 

77 

io-8g/cw3 
io~eg/c*»3 


Nothing  more  than  exhibition  of  the  order  of  values  is  intended; 
but  it  will  readily  be  seen  that  in  comparison  with  Wilson's  data  (5  =  4.3 
for  rain-like,  S  =  7-6  for  cloud-like  condensation,  and  5  =  9.9  for  the 
sensitive  tint),  the  supersaturations  here  are  enormous,  and  that  the 
condensations  must  take  place  on  something  approaching  the  molecular 
groups  of  the  system,  water — steam — air. 

It  is  therefore  scarcely  necessary  to  remark  that  the  data  are  superior 
limits,  particularly  inasmuch  as  the  influx  temperature  at  C,  fig.  50,  and 
not  the  efflux  B,  were  taken.  But  as  the  influx  of  air  is  swifter  as  the 
the  steam  pressure  increases,  the  difference  between  these  temperatures 
is  not  large.     The  escaping  steam  is  always  cool  to  the  hand. 

It  follows  that  the  color  data  bear  at  once  on  the  structure  of  dust-free 
air.  The  occurrence  of  definite  loci  for  r,  y,  g,  b,  v,  the  fact  that  any 
color  can  be  retained  indefinitely,  if  (c&t.  par.)  the  pressure-temperature 


102  VAPOR    NUCLEI    AND    IONS. 

conditions  are  fixed,  shows  that  groups  of  nuclei  counted  by  millions  per 
cubic  centimeter  must  be  available  for  condensation  long  before  the 
molecular  sizes  are  approached.  It  is  convenient  to  refer  to  the  molec- 
ular aggregates  in  question  by  the  term  "colloidal  nuclei."  They  are 
necessarily  much  smaller  than  ions.  The  number  of  such  nuclei  increases 
as  the  supersaturation  is  greater  and  the  size  needed  therefore  smaller 
until  condensation  is  actually  spontaneous  on  the  molecules  themselves. 

It  is  in  this  stage  that  one  would  naturally  expect  the  fog  particles  of 
all  sizes  to  produce  a  medium  opaque  to  transmitted  light,  as  is  actually 
the  case  provided  the  fog  particles  are  themselves  large  in  comparison  with 
the  wave-length  of  light.  It  does  not  by  any  means  follow,  however,  that 
the  turbulent  phenomenon  is  complete  at  the  lower  edge  of  the  opaque 
zone.  It  is  much  more  probable,  seeing  how  gradually  the  violet  drops 
into  the  opaque,  as  the  supersaturations  increase  with  increase  of  steam 
pressure  at  a  given  temperature  of  the  inflowing  air,  that  the  number  of 
nuclei  continually  increases.  As  this  goes  on  (*.  e.,  in  a  vertical  march 
through  the  opaque  zone)  the  time  must  arrive  when  the  fog  particles 
become  small  in  comparison  with  the  wave-length  of  light;  for  although 
the  influx  of  steam  has  increased,  the  air  influx  increases  in  the  same 
proportion.  Under  these  circumstances,  even  though  fog  particles  of 
widely  different  sizes  are  the  rule,  the  Rayleigh  effect  of  scattering  is  to 
be  looked  for. 

In  fact,  the  yellows  of  the  first  order  emerge  from  the  opaque  as  mag- 
nificently saturated  orange-browns  and  thereafter  gradually  become 
yellower.  Deep  crimson  at  the  edge  of  the  opaque  does  not  appear.  To 
prove  that  the  passage  from  blue  to  yellow  through  opaque  is  due  to  an 
increase  of  nucleation,  it  is  merely  necessary  to  add  phosphorus  nuclei, 
when  axial  violet  appears  in  the  steam  tube  at  a  sufficiently  high  tem- 
perature. Without  further  change  the  bluish  tone  at  once  passes  to 
yellow.  Again,  the  intense  oranges  above  the  opaque  may  be  obtained 
at  once  by  introducing  the  fumes  of  the  intensely  nucleating  sulphur 
flame  into  the  steam  tube.  Finally,  the  probability  of  the  Rayleigh  effect 
is  increased  by  the  fact  that  colors  of  smaller  wave-length  than  orange 
and  yellow  never  occur  above  the  opaque  zone. 

66.  Summary. — The  present  chapter  has  made  use  of  the  method  of 
testing  the  presence  and  number  of  relatively  large  nuclei  by  the 
depression  produced  in  the  terminal  asymptote  obtained  when  nucleation 
varies  with  the  drop  in  pressure,  or  of  the  diminution  in  aperture  of  the 
terminal  corona  corresponding  in  a  given  apparatus  to  dust-free  non- 
energized  air.    It  was  thus  easily  possible  to  trace  the  growth  in  number 


SUMMARY. 


I03 


of  the  persistent  nuclei  produced  by  relatively  intense  X-radiation  in  the 
lapse  of  time,  showing  results  similar  to  Chapter  I,  sections  14,  15. 

In  the  same  way  the  occurrence  of  water  nuclei  in  the  presence  of 
colloidal  nuclei  or  of  ions  was  clearly  exhibited.  These  are  due  to  the 
evaporation  of  small  fog  particles,  until  the  increase  of  vapor  pressure 
due  to  surface  curvature  is  balanced  by  the  decreased  vapor  pressure  due 
to  some  independent  phenomenon.  Hence  if  the  exhaustions  proceed 
with  a  slightly  opened  filter  cock,  such  nuclei  must  be  present  in  greater 
number  as  the  evaporation  is  faster,  because  increasingly  more  particles 
evaporate  than  subside. 

The  result  in  the  first  place  is  a  necessary  alteration  of  aperture  of 
successive  coronas,  all  other  conditions  remaining  the  same,  since  the 
large  ones  evaporate  more  fog  particles  than  those  of  lower  order  of  size 
(periodicity  of  coronal  diameter).  In  connection  with  this  phenomenon 
it  is  particularly  interesting  to  observe  that  not  only  the  colloidal  nuclei 
but  the  ions  are  available.  Questions  arise  as  to  whether  the  fog  par- 
ticles of  positive  and  of  negative  ions  evaporate  to  like  water  nuclei, 
what  becomes  of  the  charges,  since  it  is  not  clear  that  they  should  be 
dissipated,  what  phenomena  arise  from  the  decreased  mobility  of  the 
loaded  ions,  etc. 

The  means  developed  in  Chapter  II  were  again  applied  to  an  effect 
produced  (distance  effect),  when  the  radiating  source  is  removed  more 
and  more  from  the  fog  chamber.  The  results  are  necessarily  crude ;  but 
they  show  that  in  case  of  pervious  wood  fog  chambers  the  nucleations 
decrease  more  slowly  than  the  first  power  of  distance;  they  decrease 
faster  for  the  glass  fog  chamber;  faster  still  when  the  X-ray  bulb  is 
inclosed  in  a  windowed  lead  case;  fastest  when  the  window  is  closed 
with  a  thin  tin  plate;  but  in  no  case  do  they  reach  the  law  of  inverse 
squares.  All  this  points  clearly  to  the  importance  of  secondary  radiation 
in  producing  nuclei.  The  radiation  arises  both  near  the  bulb  and  near 
the  fog  chamber,  as  well  as  in  the  region  between.  The  number  of  nuclei 
produced  is  therefore  dependent  upon  an  integral  extended  over  the 
whole  interior  surface  of  the  room  and  throughout  the  intervening  air. 

In  case  of  exposure  to  weak  radium  (10  mg.  1 0,000  X)  the  asymptote 
of  dust-free  air  is  not  reached  until  the  intervening  distance  is  above  150 
cm.;  and  it  is  far  from  appearing  after  1.5  cm.  of  lead  have  been  pene- 
trated. 

The  occurrence  of  minima  of  nucleation,  when  such  weak  radium  is 
carried  from  a  long  distance  quite  up  to  the  fog  chamber,  is  again  strik- 
ingly brought  out,  provided  the  drop  of  pressure  is  sufficiently  above  the 
fog  limit  of  dust-free  air.    It  is  also  observed  when  the  ions  are  produced 


104  VAPOR    NUCLEI    AND    IONS. 

in  the  fog  chamber  by  radium  and  decay  in  the  lapse  of  time  after  the 
radium  is  suddenly  removed.  The  decay  curves  all  show  minima  for  a 
drop  of  pressure  above  the  fog  limits  of  dust-free  air;  while  the  curve  is 
normal  for  pressure  differences  below  the  fog  limit. 

If  the  coefficient  of  decay  for  the  ions  within  the  fog  chamber  is  the 
same  as  that  found  by  purely  electrical  investigations,  and  if  the  relative 
numbers  of  nuclei  corresponding  in  a  given  apparatus  and  given  con- 
ditions of  exhaustions  are  known,  then  a  new  method  for  the  standard- 
ization of  coronas  in  terms  of  the  number  of  nuclei  involved  in  their 
appearance,  is  suggested;  for 

n0  =  (n0/n-i)  bt 

if  nQ  and  n  are  two  successive  nucleations  observed  under  like  conditions 
at  t  seconds  apart  and  if  b  is  the  known  coefficient  of  decay.  Conversely, 
if  n0  is  given  this  method  lends  itself  for  the  determination  of  nucleation 
ratios  n0/n,  and  for  the  experimental  determination  of  the  distribution 
of  a  given  mass  of  precipitated  water  on  groups  of  nuclei  different  in 
average  size — one  of  the  important  of  the  outstanding  problems. 

Finally,  it  was  shown  that  data  bearing  on  the  graded  character  of  the 
colloidal  nuclei  of  dust-free  air  may  be  obtained  most  directly  and 
throughout  the  widest  range  from  the  behavior  of  the  inclosed  steam 
jet.  If  (cat.  par.)  the  steam  pressure  is  intensified  until  the  originally 
clear  field  (air  dust  being  practically  inactive),  after  passing  a  succession 
of  colors,  becomes  clear  again  in  consequence  of  absence  of  all  con- 
densation, it  follows  that  colloidal  nuclei  in  vast  numbers  and  of  contin- 
ually decreasing  size  must  successively  become  available  for  condensation 
until  the  fog  particles  are  too  small  to  be  optically  discernible.  Each 
particular  color  corresponds  to  a  group  of  colloidal  nuclei  characterized 
by  their  minimum  size.  It  is  still  to  be  determined,  however,  whether 
these  nuclei  belong  to  the  system  of  saturated  vapor,  or  to  the  air,  or  to 
both. 


CHAPTER  IV. 

DISTRIBUTION   OF  COLLOIDAL   NUCLEI  AND   OF  IONS   IN   MEDIA   OTHER 

THAN  AIR- WATER. 

COLLOIDAL  NUCLEI  AND  IONS  IN  WET  DUST-FREE  CARBON  DIOXIDE 
AND  IN  WET  COAL  GAS. 

67.  Apparatus. — The  following  experiments  were  made  with  the 
apparatus  used  in  my  last  experiments*  with  dust-free  air.  The  con- 
veyance tubes  between  the  exhaustion  chamber  (5  feet  long  and  1  foot 
in  diameter)  and  the  condensation  chamber  (18  inches  long  and  5  inches 
in  diameter)  were  about  18  inches  long  and  2  inches  in  diameter.  The 
rapid  exhaustion  thus  secured  is  effective,  but  has  by  no  means  reached 
a  limit;  there  is  still  too  much  resistance  in  the  connecting  pipes.  The 
data  obtained  with  such  an  apparatus  are  comparable  with  each  other, 
and  nothing  further  than  this  is  aimed  at,  since  in  view  of  the  very  high 
exhaustions  needed,  the  constants  for  the  computations  of  the  absolute 
nucleations  would  in  any  case  be  lacking.  It  is  a  matter  of  convenience, 
however,  to  compute  the  data  at  the  high  exhaustion  as  if  the  conditions 
met  with  at  the  low  exhaustion  were  indefinitely  applicable,  and  this  is 
the  meaning  to  be  given  to  n,  the  number  of  nuclei  per  cubic  centimeter, 
in  the  present  paper.  Moreover,  n  refers  to  the  nucleation  left  in  the 
exhausted  fog  chamber,  supposing  that  the  nuclei  are  restored  to  the  gas 
faster  than  they  can  be  withdrawn  by  exhaustion  or  that  the  nucleation 
encountered  is  fixed  for  any  definite  environment.  Otherwise  n  (to  be 
multiplied  by  the  volume  expansion)  would  be  very  much  larger. 

The  carbon  dioxide  used  was  generated  from  calc  spar  and  hydro- 
chloric acid.  The  gas  was  eventually  passed  through  a  solution  of  sodic 
hydrocarbonate,  a  long  tube  of  dry  bicarbonate  of  soda,  a  solution  of 
silver  nitrate,  and  a  calcium  chloride  drying  tube.  Then  it  entered  a 
filter  (2  feet  long),  from  which  it  was  conveyed  very  slowly  into  the  fog 
chamber.    Coal  gas  taken  from  a  gas  pipe  was  treated  in  the  same  way. 

68.  Data  for  carbon  dioxide. — In  table  42,  dp  shows  the  drop  of  pres- 
sure on  exhaustion,  5/30  (approximately)  the  angular  diameters  of  the 
coronas  when  the  eye  is  at  30  cm.  in  front  and  the  source  of  light  250 
cm.  behind  the  fog  chamber.  The  meaning  of  the  other  data  is  obvious, 
n  being  the  nucleation. 

*Phys.  Review,  xxm,  pp.  31-36,  1906. 

105 


io6 


VAPOR    NUCLEI    AND    IONS. 


Table  42. — Condensations  in  COz  generated  from  CaCo3  with  HC1.     Gas 
washed  as  specified. 


dp. 


Corona. 


n  xio- 


I.  Washed  in  water,  twice. 


31.0 

0) 

31.0 

10.7 

31.0 

7.8 

31.0 

6.4 

31.0 

5-3 

31.0 

2.7 

31.0 

2.4 

31.0 

2.0 

19. 1 

2. 1 

16.9 

2. 1 

gyo 

wr  g 
wyg 
wrg 
cor 
cor 
cor 
cor 
cor 
cor 


410 
260 
140 
100 
60 
8 

5 
2. 
2. 

2. 


II.  Washed  in  solution  of  NaHCO- 
and  AgN03. 


0 

0) 

0 

10.7 

0 

7-9 

0 

3-3 

0 

2.4 

0 

28-4 

0 

'ii. 4 

gyo 

w  o  g 

g|BP 

cor 

cor 

wrg 

wybg 


410 

305 

150 

14. 

5 
230 
380 


III.  Same,   with   long  tube  of 
NaHCO,. 


1.0 

0) 

1.0 

II  .2 

1 .0 

7-5 

1 .0 

4-3 

1.0 

4.4 

gyo 

wog 

wB  P 

cor 

cor 


410 

305 

150 

32 

33 


IV.  Same,  after  3  hours. 


31.0 

34  4 

17.6 

1  ? 

17. 1 

0  ? 

17.7 

1-2 

19.4 

1    ? 

21.2 

1-2 

24.7 

1-2 

28.O 

1 . 2 

3I.O 

2.0 

3I.O 

49.6 

cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
wrg 


33 

1 


?i 
1 


2 
240 


Corona. 


n  x  io-3. 


V.  AirbubblingthroughHCl,C02ofT 


31 


12.0 
12.0 


wybg 
wybg 

5gyo 


305 
360 
410 


VI.  Experiments  with  C02  repeated 


(6) 

11 .0 

6.4 

4.2 

;4-0 

«4.2 

2. 1 

2.0 

I 

10. 0 

3 

4 

1.8 

4 

3-2 

5 

6.7 

7 

9.8 

gyo 

wo  bg 

wrg 

cor 


cor 

cor 
wog 
green 

cor 

cor 
g'BP 
wr  og 


410 

305 
100 

29 

24 

29 

3 

2 

320 

500 

2, 

12 

140 

270 


VII.  Same. 


35o 
36.8 
38.0 
44.0 


yog 

g 

gBP 
BgBP 


400 
490 
500 
55o 


VIII.  Gas  ionized.    X-ray  bulb  at 
D  —  200  cm. 


41.7 

7-3 

35-9 

7-3 

28.8 

7-3 

27.3 

7-3 

25.8 

7-3 

24.8 

3-8 

233 

2.5 

21 .7 

1 . 1 

24.2 

4.2 

26.0 

6.8 

25-5 

5-6 

wy'g 
wog 
wog 
wog 
wog 

cor 

cor 
Just  seen 

cor 
wrg 

cor 


155 
146 
130 
125 
120 
20 

5 
1 

25 

105 

62 


1  *  given  for  successive  coronas  beginning 

with  air. 

2  CO2  off;    air  inflowing. 

3  Not  yet  air-free. 

*  Exposure  to  X-rays. 

*  No  trace  of  HC1  gas  escapes  through  the 

cleaning  train. 


6  8  given  for  successive  coronas,   begin- 

ning with  air. 

7  After  1  hour. 

8  After  2  hours ;  other  data  consecutive. 


NUCLEI    IN    WET    C02.  107 

In  parts  I  to  III  in  the  table  the  exhaustion  (dp)  is  usually  kept  con- 
stant, with  the  object  of  observing  the  behavior  of  the  mixture  of  gases, 
beginning  with  air  and  terminating  with  C02.  In  part  I  about  8  exhaus- 
tions lead  to  the  steady  behavior  of  the  latter  gas.  Inasmuch  as  the  orig- 
inal air  is  still  present  to  the  extent  of  about  i  per  cent,  an  admixture  of 
this  amount  may  be  regarded  as  inappreciable.  In  the  second  part  of 
the  table,  even  four  exhaustions,  reducing  the  air  content  to  about  n 
per  cent,  nevertheless  bring  out  the  behavior  of  C02.  The  same  things 
happen  less  certainly  in  part  III.  In  part  II,  however,  on  readmitting 
air,  two  exhaustions  nearly  suffice  to  restore  the  air  corona.  Parts  III 
and  IV  show  that  coronas  for  a  given  mixture  are  reproduced  after 
several  hours. 

The  relatively  small  coronas  obtained  with  C02  as  compared  with  air 
for  the  same  drop  in  pressure  and  in  the  same  apparatus  gave  rise  to  a 
suspicion  that  water  nuclei  associated  with  HC1  gas  might  be  involved. 
In  part  V,  therefore,  atmospheric  air  was  bubbled  through  HC1  and  the 
gas  then  passed  through  the  same  drying  train.  After  three  exhaustions 
exceptionally  high  air  coronas  were  obtained,  showing  that  the  method 
of  producing  the  gas  is  of  no  consequence,  thorough  washing  presupposed. 

Hence,  in  parts  VI  and  VII  of  the  table,  the  experiments  with  non- 
energized  CO 2  were  concluded. 

In  part  VIII  of  the  table  the  gas  is  ionized  by  the  X-rays  with  the  bulb 
at  a  distance  of  200  cm.  The  usual  constancy  of  corona  at  high  exhaus- 
tions is  observed,  while  the  fog  limit  is  exceptionally  high. 

69.  The  behavior  of  carbon  dioxide. — The  graphs  corresponding  to 
table  42  are  given  in  fig.  53,  in  connection  with  the  corresponding  data 
for  air,  both  for  the  non-energized  and  energized  states.  It  will  be  seen 
that  in  both  cases  the  curves  are  essentially  similar  in  their  contours,  but 
that  the  C02  curves  require  much  higher  exhaustion  throughout  than  the 
air  curves.  In  other  words,  the  same  coronas  occur  in  C02  as  in  air, 
provided  that  in  the  former  gas  all  the  pressure  differences  are  chosen 
to  about  5  to  5J  cm.  higher  than  in  the  case  of  air.  Similar  relations 
hold  for  the  fog  limits,  as  was  found  directly  by  Wilson*  in  a  different 
apparatus. 

The  peculiar  feature  of  these  results  is  the  degree  of  parallelism  of  the 
C02  and  air  lines,  both  for  the  non-energized  and  to  a  somewhat  smaller 
extent  for  the  energized  state.  Clearly  the  phenomena  in  both  cases  are 
alike  in  character,  though  lying  far  apart  on  the  chart. 

70.  Cause  of  differences. — In  view  of  the  more  coercible  character  of 
C02  one  would  naturally  expect  larger  colloidal  nuclei  than  in  the  case 

*C.  T.  R.  Wilson:  Phil.  Trans.  Royal  Soc,  vol.  189,  p.  288,  etc.,  1897. 


io8 


VAPOR    NUCLEI    AND    IONS. 


300 


200 


Fig.  53- — Efficient  nucleation  (n)  observed  in  media  water-air,  water- C02,  water- 
coal  gas,  energized  or  non-energized  at  different  exhaustions  dp. 

of  air,  and  it  was  with  this  anticipation  that  the  data  were  investigated. 
Taken  at  their  full  value,  however,  they  would  point  to  a  conclusion 
exactly  the  reverse  of  this.  The  colloidal  nuclei  in  C02are  apparently 
smaller  than  in  the  air,  and  the  same  is  true  {cat.  par.)  for  the  ions. 

Unfortunately  the  precise  meaning  of  these  results  is  not  clear,  for  in 
the  first  place  the  amount  of  adiabatic  cooling  may  be  written 

logr0/r=(y-i)/y.   log  p0/p 

and  thus  between  two  fixed  pressures 

log  — = const.  

The  value  of  this  fraction  is  for  air,  0.29;  for  C02,  0.22 ;  for  coal  gas,  0.19. 
In  other  words,  the  amount  of  cooling  is  less  in  C02  than  in  air  under  like 
conditions,  and  hence  the  reduced  efficiency  of  the  fog  chamber  in  the 
former  case  is  qualitatively  compatible  with  the  thermal  properties  of 
CO 2  gas.  Quantitatively,  however,  this  compensation  does  not  seem  to 
be  sufficient.  For  instance,  the  same  corona  is  obtained  in  air  and  C02 
when  the  pressure  difference  is  28  cm.  and  33.5  cm.,  respectively.     For 


NUCLEI    IN    WET    C02.  109 

like  nuclei  this  would  imply  the  same  degree  of  super  saturation.  Hence, 
if  px  and  p2  be  the  vapor  pressures  of  water  before  (200  C.)  and  after 
exhaustion,  and  p  =  j6  and  p-dp  be  the  corresponding  pressures,  the 
occurrence  of  like  supersaturation  implies  that 

Pi  /P-P2- *py  m Pi  /p-p2-dp'\Y 

P2^      P-Pi     '       P2^       P-Pi       ' 
where  pl  and  y  refer  to  C02  and  where  y  is  the  heat  ratio  for  air.     Hence 

y  _  log   (l  ~  (dj/  +  p2)/p)  -log  (l  -Pilp) 

y  log  (1  -  (dp  +pj/p)-iog  (1  -pjpy 

where  the  value  for  -  =  1.10  as  derived  for  direct  experiment. 

y 

To  compute  the  value  of  the  same  ratio  from  the  coronal  experiment 
it  is  necessary  to  know  p2  the  vapor  pressure  on  exhaustion  and  before 
condensation  ensues.  This  datum  is  unavailable,  but  it  must  be  greater 
than  o  and  less  than  would  correspond  to  the  decidedly  lower  exhaustion 
dp  =  17  (for  instance)  than  the  one  applied  (dp  =  28).     Hence  limits  of 

the  value  of  *•  may  be  computed  by  inserting  p2  =  o  and  p2  =  o.2  respect- 
ively.   The  results  are  -,  =  1.28,  both  for  the  superior  and  inferior  limits, 

as  would  be  otherwise  evident. 

One  may  summarize  these  results  as  follows:  Either  the  heat  ratio  of 
carbonic  acid,  y't  decreases  in  comparison  with  that  of  air,  y,  very  rapidly 

y 

as  temperature  decreases,   so  that  an  average  value  of —=1.3  instead 

of  -  =  1.1  is  to  be  used  in  the  preceding  experiments;  or  the  colloidal 

Y 
nuclei  in  wet  C02,  though  distributed  in  a  way  closely  recalling  the  case 

of  air,  are  throughout  smaller. 

71.  Nucleation  increases  subject  to  a  uniform  law  of  equilibrium. — The 

most  interesting  feature  of  the  data  for  C02  is  their  repetition  (under 
higher  exhaustion)  of  the  behavior  of  air.  In  other  words,  the  two  curves 
are  closely  parallel  throughout  their  extent.  This  seems  to  imply  that 
both  are  primarily  dependent,  not  on  supersaturation  or  cooling  or  on 
volume  expansion,  but  on  a  common  law  of  distribution  of  number  with 
size  of  aggregates,  such  as  is  given  by  the  theory  of  dissociation.  In 
other  words,  a  given  drop  of  pressure  of  sufficient  rapidity  and  from  a 
specific  initial  value  in  each  case  generates  the  same  number  of  colloidal 
nuclei,  though  it  does  not  follow  that  the  apparatus  in  all  cases  can 
entrap  them.  This  is  even  true  in  different  apparatus  of  different  degrees 
of  efficiency,  as  shown  elsewhere. 


no 


VAPOR    NUCLEI    AND    IONS. 


One  might  perhaps  suppose  that  cohesion  of  molecules  is  more  frequent 
when  collisions  are  less  frequent  or  that  effectively  more  large  particles 
reside  in  the  exhausted  gas.  There  are  other  cases  given  below  which 
seem  to  suggest  this  peculiar  inference. 

72.  Data  for  coal  gas. — These  are  given  in  table  43  in  the  same  way  as 
in  table  42,  both  for  the  non-energized  and  for  the  energized  gas  when 
the  X-ray  bulb  is  at  a  distance  of  200  cm.  from  the  fog  chamber.  The 
measurements  were  much  less  satisfactory  than  the  above,  the  corona 
being  thin  and  blurred.  This  may  perhaps  be  due  to  the  fact  that  mixed 
gases  are  under  examination. 

Table  43. — Distributions  of  nuclei  in  coal  gas,  washed  in  water  and  AgN03. 


dp. 

s. 

Corona. 

n  Xio-3. 

dp. 

s. 

Corona. 

nX  io-3. 

Coal  gas 

31.0 

5-i 

cor 

55 

Coal  gas 

17.6 

.0 

.0 

31.0 

5.1 

cor 

55 

19.9 

i-7 

cor 

1.7 

31.0 

5-6 

cor 

70 

31.0 

4-3 

cor 

30 

33-4 

6-7 

wyg(?) 

"5 

X-rays. 

=  200  cm. 

35-5 
40.0 

7.8 
8.9 

(Thin) 
wP(?) 

160 

250 

44.1 

9.2 

w  y' 

45o 

Coal  gas 

40.1 

6.6 

w  0  g 

121 

42.1 

10.2 

w  y 

45o 

37-8 

6.6 

w  0  g 

120 

Same. 

39-2 

yobg 

340 

35-7 

6.6 

w  0  g 

115 

38.6 

9-6 

w  b  r 

250 

32.0 

6.2 

wrg 

90 

35-3 

7-7 

w  P 

200 

30.2 

5-3 

cor 

60 

32.0 

5-3 

cor 

60 

28.6 

4-7 

cor 

40 

27-3 

3-i 

cor 

10 

27.1 

x5-2 

cor 

50 

25.8 

3-o 

cor 

9 

25-7 

4.6 

cor 

35 

24-5 

3-6 

cor 

16 

24-3 

3-4 

cor 

13 

23.2 

2.2 

cor 

3 

22.9 

2-3 

cor 

3-5 

19.4 

i-9 

cor 

2 

21.7 

i-5 

cor 

1-7 

18.4 

1.3 

cor 

1 

20.6 

l2.3 

cor 

3-i 

15.7 

.0 

0 

19.4 

.0 

cor 

.0 

1  Fluctuation  of  s  not  infrequent. 


73.  Character  of  the  early  results  for  coal  gas. — As  in  case  of  C02,  the 
data  for  coal  gas  throughout  lie  in  a  region  of  relatively  low  pressure; 
i.  e.,  large  drops  in  pressure  are  needed  to  produce  the  coronas.  Fog 
limits  are  correspondingly  high.  This  will  again  be  qualitatively  in  keep- 
ing with  the  low  heat  ratio  7. 

Apart  from  this,  these  first  results  with  the  hydrocarbon  gas  differ 
thoroughly  from  the  character  of  the  results  for  air  and  C02.  In  the  non- 
energized  gas  the  nucleations  rise  to  the  pressure  difference  at  a  rapidly 
accelerated  rate,  and  this  continues  to  the  highest  value  which  dp  applied 


NUCLEI    IN    WET   COAL-GAS. 


Ill 


and  long  after  the  air  and  C02  nucleations  have  become  stationary  in  the 
given  apparatus. 

Similarly  for  the  energized  gas  the  increase  of  nucleation  is  very 
gradual  and  the  asymptote  is  scarcely  reached  within  the  interval  dp  = 
40  cm.  of  the  experiment.  All  this  is  sharply  in  contrast  with  the  rapidity 
with  which  air  and  C02  approach  their  respective  asymptotes,  as  may  be 
seen  by  inspection  of  the  chart. 

Table  44. — Coal  gas  energized  by  X-rays  at  D  =  10  cm.  and  in  absence  of  rays.     Two- 
inch  pipes.     Lead  conveyance  tubes. 


dp. 

s. 

Corona. 

n  Xio~3. 

dp. 

s. 

Corona. 

n  Xio-3. 

32.9 

P) 

Slate  bl. 

Bulb 

removed. 

30.8 

0) 

g'G 

470 

29.0 

h 

Grayish 

27-5 

M 

Grayish 

19.4 

.0 

0.0 

26.0 

11 

w  y  ' 

340 

22.4 

0 

.0 

21.7 

5-7 

w  r  ' 

58 

24.6 

? 

0 

.0 

20.6 

3 

5 

cor 

13 

26.0 

1 

7 

2.2 

18.2 

2 

1 

cor 

2.3 

27.9 

3 

8 

21.5 

16.9 

0 

.0 

30.1 

6 

4 

w  y 

97 

24.0 

10 

5 

wy  0 

260 

31.2 

7 

3 

w  be 

137 

22.7 

7 

8 

g'B 

125 

32.8 

9 

5 

wr  0 

270 

21.5 

5 

4 

w  r 

50 

34-8 

10 

4 

w  y 

400 

37-3 

?w  y ' 

410 

Coronas  too  vague  for  measurement. 


74.  New  data  for  coal  gas. — In  case  of  the  above  results  the  large 
vacuum  chamber  was  not  quite  filled  with  coal  gas  and  there  may  have 
been  diffusion  from  one  vessel  to  the  other.  Again,  the  rubber  connecting- 
tubes  of  the  first  experiment  (though  in  advance  of  the  filter)  were 
replaced  by  lead  connecting-tubes,  as  rubber  is  pervious  to  coal  gas. 
Whether  from  these  causes  or  others,  the  results  came  out  quite  differ- 
ently after  every  part  of  the  apparatus  had  been  filled  with  coal  gas. 
This  is  also  shown  in  fig.  52  and  the  results  themselves  are  inserted  in 
table  44. 

The  new  results  for  coal  gas  now  conform  in  character  with  the  data 
for  media  of  air-water  and  carbon  dioxide-water,  and  for  the  non-ener- 
gized state,  the  coal-gas  line  lies  between  the  curves  for  the  other  two 
media,  as  the  figure  shows.  In  like  manner  the  curve  for  coal  gas  ener- 
gized by  the  X-rays  now  betrays  nothing  abnormal.  In  endeavoring 
to  discover  reasons  for  the  differences  between  the  data  of  table  43  and 
table  44,  the  presence  of  rubber  tubing  in  the  former  case  comes  nearest 
to  suggesting  a  solution.  Carbon  disulphide  emits  nuclei  spontaneously; 
whether  these  may  pass  through  the  filter  has  not  been  tested ;  but  it  is 


112  VAPOR    NUCLEI    AND    IONS. 

conceivable  that  the  action  of  coal  gas  on  vulcanized  rubber  may  in  a 
somewhat  similar  way  to  carbon  disulphide  be  productive  of  nuclei. 

If  these  are  larger  than  colloidal  nuclei,  though  they  may  still  be 
much  smaller  than  ions,  they  would  pass  through  the  filter  and  give  rise 
to  the  very  phenomenon  of  depression  of  asymptote  observed  in  table  43. 

75.  Conclusion. — Neither  from  the  cases  of  C02  nor  of  coal  gas  does  it 
follow  that  coercible  gases  have  larger  colloidal  nuclei  than  non-coercible 
gases  like  air.  The  apparent  results  are  the  reverse  of  this.  If  the 
increased  difficulties  of  condensation  in  the  former  are  due  to  smaller 
heat  ratios  (y)  as  compared  with  air,  there  is  no  reason  why  C02,  where  y 
is  larger,  should  show  greater  condensation  difficulties  than  coal  gas 
where  y  is  smaller.  The  distributions  of  nuclei  suggest  a  common  law 
of  dissociation  or  chemical  equilibrium. 


COLLOIDAL  NUCLEI  AND  IONS  IN  DUST-FREE  AIR  SATURATED 
WITH  ALCOHOL  VAPOR. 

76.  Introductory. — In  my  report*  on  the  solutional  nucleus  and  else- 
wheref  I  came  to  the  conclusion  that  the  differences  in  promoting  con- 
densation exhibited  by  positive  and  negative  ions  were  more  probably 
to  be  ascribed  to  the  difference  in  chemical  structure  or  composition 
involving  a  difference  of  size  than  to  the  electrical  differences  as  such. 
Experiments  made  in  Wilson 's  apparatus  by  Dr.  Donnan  J  with  vapors 
of  methyl  and  ethyl  alcohol,  carbon  tetrachloride,  carbon  disulphide, 
benzol,  and  chlorobenzol  show  that  the  supersaturation  needed  to  produce 
condensation  was  not  necessarily  greater  in  ionizing  than  in  non-ionizing 
solvents.  With  similar  apparatus  Dr.  K.  Przibram§  recently  examined 
a  series  of  alcohols  and  other  bodies  ionized  by  the  X-rays,  obtaining 
among  a  variety  of  data  a  noteworthy  result  with  a  direct  bearing  on  the 
question  here  at  issue.  It  appears  that  whereas  in  the  case  of  water 
vapor  the  negative  ions  are  more  efficient  condensation  nuclei  than  the 
positive  ions,  the  reverse  holds  for  the  alcoholic  vapors.  In  cases  of 
methyl,  ethyl,  amyl,  and  heptyl  alcohols  (including  some  other  bodies 
like  chloroform)  the  positive  ions  invariably  require  less  supersaturation 
to  precipitate  condensation  than  the  negative  ions  of  the  same  body. 

Interesting  differences  are  therefore  manifest  in  the  behavior  of 
vapors,  and  it  seemed  desirable  to  test  the  nucleation  of  a  medium  of 

*  Structure  of  the  Nucleus.     Smithsonian  Contrib.,  No.  1373,  p.  161,  1903. 

t  Ions  and  Nuclei,  Nature,  lxix,  p.  103,  1903. 

X  F.  G.  Donnan:  Phil.  Mag.  (6),  ill,  pp.  305-310,  1902. 

5  K.  Przibram:  Wien  Sitzungsber.,  cxv,  pt.  ua,  pp.  1-6,  1906.  •   ' 


NUCLEI    IN    ALCOHOL    VAPOR.  113 

ethyl  alcohol  and  air  in  comparison  with  the  media  of  water-air  and 
water-carbon-dioxide  hitherto  examined.  The  former  behaves  in  fact 
as  if  the  nuclei  were  throughout  larger  than  in  the  latter  cases. 

77.  Apparatus  and  method. — The  experiments  were  conducted  with 
an  apparatus  in  which  the  connecting  pipes  between  the  fog  chamber 
(18  inches  long,  5  inches  in  diameter)  and  the  vacuum  chamber  (5  feet 
long,  1  foot  in  diameter)  were  4  inches  in  diameter,  containing  a  4-inch 
counterpoised  plug  stopcock.  The  whole  connecting  system  was  about 
22  inches  long,  one-half  of  it  belonging  to  the  fog  chamber.  Experiments 
made  with  water  vapor,  however,  did  not  show  any  further  marked 
advantage  arising  from  the  use  of  the  large  passage-way  specified,  over 
the  former  apparatus,  in  which  the  corresponding  tube  was  2  inches  in 
diameter.  It  is  therefore  superfluous  to  adduce  for  comparison  the  new 
data  for  water  vapor.  The  general  method  for  work  was  that  frequently 
described  in  connection  with  these  investigations. 

78.  Properties  of  alcohol  fog. — While  the  experiments  of  my  preceding 
paper  with  the  medium  of  water  vapor  and  carbon  dioxide  gas  showed 
unusually  high  values  of  the  exhaustions  needed  to  produce  coronal 
condensation,  the  case  of  alcohol-air  shows  correspondingly  low  values 
of  exhaustion  as  compared  with  those  for  water-air.  The  number  of  col- 
loidal nuclei  entrapped  by  alcohol  vapor  are  about  3.5  times  larger  than  is 
the  case  for  water  vapor  under  like  conditions.  Hence  the  coronas  for 
alcohol  are  exceedingly  dense  by  contrast.  They  are  also  much  less  pure 
in  color,  and  particularly  at  high  exhaustions  become  fog-like.  The 
phenomenon  is  coarsened  and  measurement  less  satisfactory. 

As  the  alcohol  fog  particles  are  larger  in  size,  they  subside  more  rapidly 
at  the  same  exhaustion  than  water  particles;  but  the  occurrences  are 
in  the  former  case  far  from  simple.  While  the  corona  (if  not  too  large) 
remains  nearly  the  same  throughout  the  slow  subsidence  of  water  parti- 
cles, the  corona  for  alcohol  particles  decreases  one-half  or  more  in  size 
during  this  period.  In  other  words,  the  alcohol  particles  experience 
very  rapid  growth  during  subsidence,  from  which  it  follows  that  many  of 
them  must  evaporate  to  compensate  in  part  for  the  eight-fold  or  more 
enlargement  in  bulk  of  the  survivors.  The  same  fact  may  account  for 
the  blurred  coronas;  for  the  true  initial  corona  being  very  evanescent 
is  probably  not  seen.  Conformably  with  this  view  it  is  impossible  to 
exceed  large  white-reddish  forms  in  the  present  apparatus  and  to  reach 
the  high  greens  observed  with  water  vapor. 

79.  Number  of  particles. — In  order  to  determine  the  number  of  particles 
corresponding  to  a  given  corona,  it  is  first  necessary  to  compute  the 
amount  of  alcohol  precipitated  per  cubic  centimeter  of  the  exhausted 


ii4 


VAPOR    NUCLEI    AND    IONS. 


vessel  by  the  sudden  cooling  incident  upon  exhaustion.  This  may  be 
done  by  a  straightforward  approximation*  with  results  shown  in  the 
following  table,  45,  where  tt  is  the  initial  temperature  of  the  saturated  air 
within  the  fog  chamber,  t2  the  temperature  after  sudden  exhaustion  and 
before  condensation,  and  t  the  temperature  after  the  precipitation  of  the 
m  grams  of  alcoholic  fog  per  cubic  centimeter.  The  drop  in  pressure  is 
dp  from  p  =  76  cm.  at  200  C.  The  data  of  the  last  column  will  be  presently 
explained. 

Tabl,k  45. — Precipitation  of  alcohol  vapor  at  different  exhaustions  (dp),  super- 
saturations  (5),  and  radius  (r),  of  nuclei. 


dp. 

4- 

t2. 

t. 

m  Xio6. 

S-fr/p+. 

r  X  io7. 

cm. 

10 
20 
30 

0 

20 
20 
20 

0 

+  3-2 
-15-3 
-36.1 

0 

+  14.8 
+ 10.  2 
+   3.2 

Grams. 
10. 0 

18.3 

22.8 

2.42 
6.  21 
21.4 

cm. 
1.44 

•75 
.48 

These  may  be  compared  with  the  case  of  water  vapor. 

8.5 
17 
22 

30 

20 
20 
20 
20 

+  5-8 
-  9.6 
-18.9 
-36.1 

+  14.7 
+   8.8 
+   4.6 
-    3-5 

2.6 
4.6 
5-5 
6.4 

2.17 
5-68 

69.7 

165 

•77 
•58 
•35 

We  may  infer  from  the  table  that  in  a  perfect  apparatus  and  for  true 
pressure  differences!  water  fog  particles  would  reach  freezing  (o°  C.)  at 
^  =  24  cm.  and  alcohol  fog  particles  at  ^  =  34.5  cm.  Moreover,  for  the 
same  corona  there  must  be  on  the  average  about  3.5  times  more  particles 
in  the  alcoholic  fog  than  in  the  water  fog,  which  accounts  for  the  opaque- 
ness of  the  former. 

For  the  reasons  adduced  it  is  not  worth  while  to  express  the  results 
otherwise  than  in  round  numbers,  for  the  data  involved  are  inevitably 
crude.  The  assumption  of  the  law  of  adiabatic  cooling  as  far  as  -  3 6°  C. 
is  questionable,  in  view  of  the  admixture  of  saturated  vapor;  but  as  the 
densities  of  vapor  are  for  alcohol  about  8  per  cent  that  of  air  and  for 
water  vapor  about  7  per  cent,  this  approximation  in  a  rarefied  atmos- 
phere like  the  use  of  Boyle's  law  for  a  wet  gas  is  probably  admissible. 
It  is  different,  however,  with  the  latent  heat  of  the  vapor,  which  is 
required  at  the  low  temperatures,  but  is  known  (as  a  rule)  only  at 
temperatures  near  the  boiling-point.     From  this  and  similar  points  of 

*  C.  T.  R.  Wilson:  Phil.  Trans.,  London,  vol.  189,  1897,  P-  300. 

f  dp  computed  as  p-p2  in  the  way  shown  in  Chapter  II,  and  not  the  apparent  value 
observed  at  the  fog  chamber. 


NUCLEI  IN  ALCOHOL  VAPOR.  115 

view,  measurements  of  latent  heat  for  the  more  common  vapors  at  very 
low  temperatures  would  be  desirable. 

Finally,  the  point  at  which  the  drop  in  pressure  ceases  to  be  efficient, 
on  account  of  the  increasingly  rapid  inward  radiation  of  heat  from  the 
vessel,  is  the  most  serious  of  the  outstanding  errors.  I  have  endeavored 
to  diminish  it  compatibly  with  the  desideratum  of  a  large  and  easily 
adjusted  fog  chamber  by  successively  increasing  the  bore  of  the  exhaust 
pipes  and  stopcocks;  and  this  plan  has  been  in  the  large  measure  suc- 
cessful. The  extent  to  which  the  error  is  present,  as  the  drop  in  pressure 
increases  more  and  more,  is  nevertheless  left  unanswered.  If  the  upper 
inflection  of  the  distribution  curve  (fig.  56)  is  a  criterion,  i.e.,  the  occur- 
rence of  identical  terminal  coronas  for  successively  increasing  exhaus- 
tions, the  fog  chamber  with  water-air  is  efficient  to  about  dp  =  31  or  32 
cm.,  with  water  and  carbon  dioxide  to  about  dp  =  37  cm.,  with  alcohol 
and  air  to  about  dp  =  20  cm.  In  the  former  case  the  vapor  would  be 
cooled  from  200  to  about  —  io°  C.  even  after  condensation;  in  the  latter 
case  to  about  +io°.  On  general  principles  and  in  view  of  the  low 
temperature  of  the  water,  it  would  seem  probable  that  the  efficiency  of 
the  fog  chamber  must  vanish  gradually.  But  the  appearance  of  the 
curves  is  such  as  if  the  action  were  unimpaired  up  to  a  given  terminal 
drop  in  pressure. 

In  every  case  the  fog  particles  with  the  surrounding  medium  of  vapor 
soon  reach  the  temperature  of  the  air  again,  so  that  additional  moisture 
must  arrive  from  somewhere.  It  is  remarkable  that  the  marked  con- 
stancy of  the  water  coronas  in  perfectly  tight  apparatus  during  this 
period  gives  no  evidence  of  the  evaporation;  while  the  alcohol  coronas 
decrease  one-half  in  aperture  or  the  preponderating  fog  particles  actually 
grow.  Even  if  this  is  compatible  with  the  evaporation  of  the  smaller 
particles,  there  is  again  no  evidence  for  it.  Much  of  the  moisture  must 
therefore  come  from  the  wet  cloth  and  the  water  within  the  vessel,  which 
are  not  cooled  by  the  expansion. 

80.  Size  of  the  nuclei. — Here  it  may  be  worth  while  to  inquire  into  the 
reason  why  the  precipitation  in  alcohol  is  apparently  so  much  easier; 
or,  what  is  the  same  thing,  into  the  estimated  size  of  the  nucleus  on  which 
precipitation  takes  place  in  these  several  cases.  The  Kelvin  equation 
as  modified  by  Helmholtz*  may  be  used  for  this  purpose,  as  was  done  by 
the  latter  and  by  Wilson  t  in  the  form  pT/pM  =e2T/Rsdr  where  pr  and 
pM  are  the  vapor  pressures  at  the  convex  areas  of  radius  r  and  radius 
infinity,  respectively,  T  the  surface  tension  of  the  liquid  of  density  (s), 
R  the  gas  constant  of  its  vapor  at  the  absolute  temperature  (#) . 

*  Helmholtz:  Weid.  Ann.,  xxvn,  p.  524,  1886. 
f Wilson:  Phil.  Trans.,  vol.  189,  p.  305,  1897. 


n6 


VAPOR     NUCLEI    AND    IONS. 


Fig.  54. — Supersaturations  (S)  of  media  air-water 
and  alcohol -water,  and  estimated  radius  (r  cm.) 
of  smallest  efficient  nuclei,  at  different  exhaus- 
tions (dp),    m,  molecular  radius.     Table  45. 


Since  pT  is  the  adiabatically 
reduced  vapor  pressure  (with- 
out condensation)  in  the  vol- 
ume expansion  due  to  the 
drop  of  pressure  (dp)  and  pM 
the  normal  vapor  pressure  at 
the  same  temperature  (?9  = 
2  7  3°  +  *2  m  table  1),  r  follows 
from  the  equation.  The 
values  of  prlpw  and  r  so  found 
are  both  given  in  table  45, 
and  have  been  constructed  in 
the  chart  (fig.  54),  where  their 
relation  to  the  usual  order  of 
molecular  size  is  also  indi- 
cated. Clearly  these  values 
of  r,  the  radius  of  the  nuclei 
differing  so  little  from  molec- 
ular radii  (say  io~8),  can  only 
indicate  an  order  of  values; 
for  apart  from  the  difficulties 
above  enumerated  in  com- 
puting #,  r  depends  on  sur- 
face tension  (T),  which  has  no 
meaning  for  molecular  dimen- 
sions. Granting  this,  it  is 
none  the  less  remarkable  that 


the  values  of  r  obtained  should  be  so  nearly  alike  for  water  and  alcohol 
where  different  constants  (T,  R,  s,  etc.)  occur  throughout;  in  other 
words,  that  at  a  given  temperature  a  given  drop  of  pressure  will  condense 
both  vapors  on  nuclei  of  about  the  same  size. 

In  so  far  as  these  estimates  are  admissible  it  follows  that  the  alcohol- 
air  nucleus  is  larger  than  the  water-air  nucleus,  since  in  the  former  case 
coronal  condensation  begins  at  about  dp  =  i$  cm.  where  r  =  io~7  cm. 
and  in  water  vapor  it  begins  at  dp  =  26  cm.  where  r=  4  X  io~8  cm.  about, 
less  than  half  as  large.  These  relations  once  established  are  retained 
through  all  successions  of  nuclei,  as  the  following  data  for  alcohol  vapor 
in  comparison  with  water  vapor  show.  It  is  a  little  difficult  to  under- 
stand why  the  ionized  nuclei  in  alcohol  vapor  should,  like  the  colloidal 
nuclei,  be  larger  than  the  corresponding  cases  for  water  vapor,  unless  the 
ions  are  aggregated  vapor  nuclei,  a  point  of  view  tentatively  advanced 
elsewhere;   but  this  larger  alcohol  nucleus  suggests  that  it  is  primarily 


NUCLEI    IN    ALCOHOL    VAPOR.  II 7 

Table  46. — Colloidal  nuclei  and  ions  in  alcohol  vapor,  energized  or  not;    4-inch  cock. 


dp. 

s. 

Corona. 

n  X10-*. 

I.    April  23.     Not  energized 

30.8 

28.4 

10 

iwr> 

1,060 

10 

iwr' 

1,005 

26.0 

10 

iw  r' 

950 

23.0 

11 

1W  y' 

1,100 

21. 1 

10 

'w  c 

615 

19. 1 

7-7 

gBP 

385 

17-3 

4.8 

cor 

108 

16.0 

2.4 

cor 

11 

4-7 

1-5 

cor 

4 

13-4 

1.1 

cor 

3 

12.3 

(?) 

(2) 

0 

10.2 

(?) 

(3) 

0 

19.9 

(?) 

(') 

0 

12.7 

0 

(2) 

0 

16.7 

5-o 

cor 

"5 

18.5 

7-7 

gBP 

380 

20.0 

10.5 

w  r' 

680 

I 1 ,   April  24 

34-0 
42.0 

10 

xwr' 

940 
1,040 

10 

*wr' 

38.8 

11 

2w  0' 

1,170 

34-2 

11 

*w  0' 

1,110 

32.2 

11 

'wo' 

1,080 

29-3 

12 

'w  y' 

1,270 

26.8 

'wy' 

1,210 

24.0 

lw  y' 

1,120 

21.9 

11 

'wr' 

720 

20.0 

10 

lw  c 

600 

18.3 

8.2 

wy 

340 

16.7 

3-5 

cor 

38 

15.0 

1.0 

cor 

3 

Later 

14.8 

1 

cor 

3 

16.3 

5-o 

3wr' 

"5 

18.3 

7-6 

w  y  b 

320 

19-5 

9.0 

w  r' 

585 

21.7 

10.5 

w  r' 

720 

22.0 

10.5 

w  r' 

740 

April  25 

26.0 

12 

w  y' 
wy' 
w  y' 

1,190 
1,160 

I XI.  X-rays  on.     D  •=•  15  cm 

25.2 
17.7 

4I2 

12 

920 

151 

II 

w  r' 

650 

14.0 

8.4 

w  y  B 

275 

12.9 

2.6 

cor 

13 

11. 5 

•5 

(?) 

0 

11. 5 

.O 

(?) 

0 

X-rays  off 

11 .0 

5.o 

0 

IV.  X-rays  on.    D  =  15  cm 

12.4 
13.2 

5.o 

0 

5.1 

cor 

IOI 

14.2 

8.1 

w  B  P 

275 

151 

10. 

w  r' 

490 

16. 1 

10.5 

w  r' 

580 

April  26 

36.6 

11 

w  y' 

1,420 

1  Accompanied  by  dense  fogs,  rapidly  sub- 
siding, with  coronas  dwindling. 
1  Small  coronas  probably  due  to  shaking. 
8  All  coronas  accompanied  by  dense  fogs. 


*  Coronas  decreased  in  size  during  sub- 
sidence, more  than  one-half. 

•Coronas  often  due  to  solutional  nuclei; 
produced  by  shaking. 


n8 


VAPOR    NUCLEI    AND    IONS. 


30 


16  18  20  22  24  26  28 

Fig.  55. — Aperture  of  coronas  (s),   observed  at  different  exhaustions  (dp),  in  media  of 
alcohol-air,  water-air,  energized  or  non-energized.     Table  46. 


0.y 

FIG. 

56 

ggarr" 

t\ 

*** 

Jfj, 

/ 

/ 

ALCOHi 

■>L  -AIR 

/i 

1 

H 
if 

1 

oA 

WATER 

3 

TlYlO'3 

A 

,4 

\  1 
/ 

/o  " 

£- — 

*/ 

#/ 

-t& 

A 

0 

/ 

+*p 

10  12  14  16  18  20  22  24  26  28  30  32  34  36  38 

Fig.  56. — Efficient  nucleation  n  in  energized  or  non -energized  media  of  alcohol-air  and 
water-air,  at  different  exhaustions  {dp).     Table  46. 


the  saturated  vapor  which  furnishes  the  colloidal  nuclei  and  that  the 
gas  is  only  secondarily  involved. 


81.  Data  for  alcohol  vapor. — The  behavior  of  alcohol  vapor  is  shown 
in  the  usual  way  in  table  46,  where  dp  is  the  sudden  fall  in  pressure  from 
atmospheric  pressure  producing  the  corona  of  the  angular  diameter 
5/30,  when  the  eye  and  the  source  of  light  are  at  distances  40  and  250 
cm.  on  the  opposed  sides  of  the  fog  chamber.  The  nucleation  n  is  com- 
puted in  the  way  given  above,  section  79,  and  indicates  the  number  of 


NUCLEI  IN  ALCOHOL  VAPOR.  119 

nuclei  in  the  exhausted  fog  chamber.  It  is  assumed,  therefore,  that  the 
nuclei  are  reproduced  more  quickly  than  they  can  be  withdrawn  by  the 
exhaustion.  Measurement  of  j  is  not  very  satisfactory,  as  the  coronas 
are  blurred  and  accompanied  by  dense  fogs  and  changes  rapidly  on 
subsidence.  The  effect  of  X-radiation  is  shown  in  parts  III  and  IV  of 
the  table  leading  to  the  same  terminal  corona  as  for  the  non-energized 
vapor. 

The  results  have  been  given  graphically  in  figs.  55  and  56,  the  former 
referring  to  coronas  (s),  the  latter  to  nuclei  (w),  in  connection  with  earlier 
results  for  media  of  water-air  and  water-carbon  dioxide,  the  same  con- 
densation apparatus  and  method  underlying  all  experiments.  One 
may  notice  at  once  that  in  the  cases  C02-water  and  air-water,  both  for 
the  non-energized  and  for  the  energized  state,  the  observed  data  would 
be  obtained  by  shifting  the  air-water  diagram  as  a  whole  to  the  right, 
as  if  the  cooling  in  case  of  C02-water  vapor  were  less  efficient.  The 
graphs  are  of  the  same  kind,  nearly  parallel,  and  all  of  them  (energized 
or  not)  terminate  in  the  same  asymptote  or  large  green-blue-purple 
corona. 

The  alcohol  curves  are  different  from  these  chiefly  in  three  respects:  (1) 
Though  the  graphs  both  for  the  non-energized  and  energized  states  again 
terminate  in  the  same  asymptote,  this  is  not  the  green-blue-purple 
corona,  but  the  white-yellow  corona  which  lies  slightly  below  it;  (2)  the 
curves  as  a  whole  lie  with  a  somewhat  larger  slope  in  a  region  of  much 
lower  exhaustions  (dp);  (3)  the  number  of  nuclei  caught  in  alcohol 
vapor  is  relatively  very  large.  The  second  and  third  observations  have 
already  been  discussed.  The  first  deserves  especial  consideration.  The 
question  occurs  at  once  why  both  the  energized  and  the  non-energized 
curves  should  terminate  in  the  same  final  corona,  irrespective  of  the 
size  of  the  nuclei,  and  why  this  should  be  lower  for  alcohol  than  for 
water.  For  the  ionized  state  one  might  infer  that  the  total  number  of 
ions  has  been  precipitated,  as  is  actually  the  case  for  low  ionization; 
but  if  for  strong  ionization  this  were  true  for  alcohol  vapor  it  could 
not  be  true  for  water  vapor  where  the  number  of  ions  caught  is  less  than 
one-half  the  number  in  alcohol.  In  general,  it  is  improbable  that  the 
terminal  corona  for  ions  should  in  such  a  case  be  the  same  as  the  terminal 
corona  for  colloidal  nuclei. 

The  explanation  which  seems  plausible  to  me  is  this:  Each  nucleus 
must  drain  the  air  of  its  supersaturated  moisture  within  a  certain  radius, 
large  as  compared  with  the  size  of  the  nucleus  and  increasing  in  the 
lapse  of  time. 

A  limit  of  the  phenomenon  will  be  reached  when  for  an  indefinite 
number  of  graded  nuclei  the  enveloping  spheres  free  from  supersatu- 


120  VAPOR    NUCLEI    AND    IONS. 

ration  form  a  system  in  contact.  In  case  of  water  vapor  the  distance 
between  centers  would  be  0.014  cm.;  in  case  of  alcohol  0.010  cm.,  dis- 
tances which  are  both  enormous  as  compared  with  the  estimated  size 
of  nuclei  (r,  table  45,  fig.  54).  The  greater  distance  which  belongs  to 
water  vapor  would  be  in  keeping  with  its  greater  diffusivity,  though  this 
surmise  does  not  work  out  for  water-carbon  dioxide  as  compared  with 
water- air.  At  all  events,  when  the  limiting  number  of  nuclei  has  been 
captured,  the  apparatus  is  powerless  to  produce  condensation  on  a 
greater  number  of  nuclei,  be  they  relatively  large  as  the  ions  or  small 
as  the  colloidal  nuclei,  however  many  other  inefficient  nuclei  may  be 
present. 

ABSENCE  OF  COLLOIDAL  NUCLEI  IN  STRONG  ODORS. 

82.  Introductory. — Throughout  the  course  of  my  work  I  have  been 
endeavoring  to  find  whether  bodies  with  strong  odors  and  presumably 
large  molecules  could  be  regarded  as  a  source  of  colloidal  nuclei;  or 
whether  there  is  any  relation  between  the  colloidal  nucleus  and  the 
odors.  In  case  of  carbon  disulphide,  from  which  nuclei  apparently 
escape  spontaneously,  this  would  seem  to  be  the  case;  but  it  is  yet  to  be 
proved  that  vapor  of  carbon  disulphide,  if  carefully  filtered,  neverthe- 
less still  produces  colloidal  nuclei  in  the  fog  chamber.  In  the  present 
instance  it  is  not  improbable,  if  relatively  few  CS2  molecules  are  oxidized 
SO 3,  that  sulphuric  acid  nuclei  are  the  result.  The  experiment  which 
has  already  been  discussed  is  well  worth  while ;  but  I  did  not  make  it, 
in  the  fear  of  contaminating  the  vacuum  chamber.  The  following  experi- 
ments show,  however,  that  even  in  the  extreme  cases  odors  are  due  to 
molecules,  and  that  in  relation  to  the  fog  chamber,  apparently  large  mole- 
cules are  still  quite  negligibly  small  in  comparison  with  the  colloidal 
nuclei. 

83.  Data  for  camphor,  turpentine,  naphthalene. — The  results  obtained 
are  given  in  table  47  in  the  usual  way.  The  glass  fog  chamber  was 
provided  with  a  hole  in  the  (thick)  bottom,  about  2  cm.  in  diameter 
and  closed  with  a  rubber  cork.  It  was  free  from  leakage  from  without. 
The  bodies  to  be  examined  were  introduced  through  the  hole  in  question, 
and  suspended  in  the  middle  of  the  fog  chamber  by  aid  of  a  wire-gauze 
tube  20  cm.  long  and  2  cm.  in  diameter.  After  putting  this  tube  in 
place  the  air  was  carefully  cleansed  by  precipitation  of  dust. 

On  May  5,  6,  and  7,  after  putting  the  apparatus  together,  the  medium 
within  was  first  examined  without  introducing  the  odoriferous  body. 
The  internal   sources   of  spurious  nucleation   gradually   vanish.     The 


NUCLEI    IN    STRONG    ODORS. 


121 


Table  47. — Miscellaneous  experiments.     Water  nuclei  effect  of  metal  surfaces,  of  odors, 
etc.    dp  =/>  -  p3.     Four-inch  pipes  and  plug  cock. 


Date,  etc. 


dp. 

s. 

Corona. 

n  X 10-8. 

30.8 

9.4 

wrg' 

240 

30.6 

'6.5 

cor 

105 

30.8 

IO.O 

wrg' 

260 

30.8 

12.0 

wy  bg 

380 

30.8 

*ll.O 

wrg 

275 

30.8 

II  .0 

wrg 

275 

30.5 

10.0 

wpg 

230 

30.6 

II  .0 

wy'g 

380 

30.7 

II 

wrg 

305 

30.6 

II 

wrg 

275 

30.8 

1 1 

wog 

305 

30.8 

II 

wyg 

380 

30.8 

13 

g'  to  gy 

410 

30.8 

13 

g' 

455 

30.8 

13 

g'  to  gy 

425 

30.6 

13 

g'  to  gy 

425 

30.6 

12 

yo 

410 

30.7 

(3) 

gyo 

410 

30.6 

13 

gtogy 

425 

30.6 

13 

gBP 

455 

30.8 

13 

gBP 

455 

May  5.     Wet  cloth  lining  in  exhaust  tube 

May  6 

May  6 

May  7 

Examination  of  odors:3 

May  8.     Air  only 

May  9.     Air,  camphor  in 

May   10.     Camphor 

May   11.     Camphor 

Air  without  camphor 

May    12.     Air 

May    13.     Turpentine 

May   15.     Naphthalene4 , 


1  Foreign  nuclei  not  absent  in  second  exhaustion. 

2  Hole  drilled  in  bottom  of  glass  fog  chamber,  closed  by  rubber  cork. 

3  Apparatus  blurred. 

4  Enlargement  of  coronas  due  to  second  (smaller)  exhaustions. 

exhaust  pipes  were  cloth-lined  and  the  cloth  kept  wet  to  guard  against 
minor  saturation  error.  On  May  8,  with  the  introduction  of  camphor, 
the  nucleation  apparently  rises  to  a  maximum  (g-b-p.  corona) ;  but 
the  same  result  is  maintained  after  the  removal  of  the  camphor  and  the 
gauze  (tested  in  many  observations  not  recorded  in  the  tables).  Hence 
the  camphor  nuclei  can  not  be  larger  than  the  colloidal  nuclei  of  air- 
water;  for  the  presence  or  absence  of  camphor  within  a  fog  chamber  is 
inappreciable.  The  same  conclusion  follows  from  the  experiments  with 
turpentine  (where  the  walls  of  the  fog  chamber  were  speedily  blurred 
from  distillation  of  small  quantities  out  of  the  lamp  wick  holding  the 
liquid)  and  from  naphthalene.  It  is  fair  to  conclude  that  presumably 
large  molecules  are  nevertheless  bodies  of  an  inferior  order  of  size  rela- 
tive to  the  colloidal  nuclei  of  dust-free  air. 


84.  Summary. — Media  of  coal  gas  and  water  require  higher  exhaustion 
than  media  of  air  and  water,  media  of  carbon  dioxide  and  water  higher 
than  coal  gas  and  water,  to  precipitate  condensation  in  like  degree, 


122  VAPOR    NUCLEI    AND    IONS. 

other  things  being  equal.  On  the  other  hand,  media  of  alcohol  and  water 
require  smaller  exhaustion  to  precipitate  an  alcohol  fog  in  corresponding 
degree.  The  general  character  of  the  phenomena  in  all  these  several 
cases  are,  however,  the  same.  Their  relation  to  each  other  when  the 
media  are  energized  in  like  manner  by  the  X-rays  is  also  the  same. 
(Pf.  fig.  56.) 

It  does  not  follow,  therefore,  that  wet  coercible  gases  like  carbon 
dioxide  and  coal  gas  contain  larger  colloidal  nuclei  than  wet  air.  The 
apparent  result  would  be  quite  the  reverse  of  this.  Neither  can  the 
difference  be  explained  in  terms  of  the  respective  value  of  the  ratio 
of  specific  heats  (y);  for  in  relation  to  condensation,  the  order  is  air,  coal 
gas,  carbon  dioxide;  in  relation  to  y,  air,  carbon  dioxide,  coal  gas.  The 
probable  occurrence  of  large  colloidal  nuclei  in  media  of  alcohol  and  air 
and  relatively  small  colloidal  nuclei  in  water  and  air  seems  to  show  that 
the  colloidal  nuclei  are  primarily  to  be  associated  with  the  saturated 
vapor,  and  that  the  gas  involved  is  of  secondary  importance.  It  can 
not  be  a  question  of  mere  solubility  of  gas  in  the  vapor,  for  this  is 
strongest  in  water  and  carbon  dioxide,  in  which  there  is  no  evidence  of 
large  nuclei.  The  curves  of  distribution  of  number  with  size  are  again 
such  as  to  suggest  a  common  law  of  equilibrium. 

The  presence  of  strong  odors  (camphor,  naphthalene,  turpentine,  etc.) 
in  the  fog  chamber  is  without  an  appreciable  effect.  Hence  the  col- 
loidal nuclei  can  not  be  large  molecules  merely,  and  colloidal  nuclei  can 
not  be  ascribed  to  chemical  impurities  in  the  gas. 

Continued  slow  exhaustion  seems  to  be  favorable  to  the  growth  of 
fog  particles  and  the  formation  of  rain. 

Both  for  the  energized  and  for  the  non-energized  state,  the  graphs 
for  the  same  media,  though  referring  to  nuclei  of  widely  differing  sizes 
(ions,  colloidal  nuclei),  again  terminate  in  the  same  asymptote,  or  end 
in  the  same  terminal  corona.  This  is  not  identical  for  different  media, 
however,  the  corona  being  of  lower  order  though  denser  for  alcohol 
and  air,  of  higher  order  but  thinner  for  water  and  air,  for  instance.  The 
number  of  nuclei  caught  {cat.  par)  in  alcohol  and  air  is  much  larger  than 
in  water  and  air.  When  the  limiting  number  of  nuclei  has  been  reached 
by  condensation,  the  system  is  powerless  (in  a  given  apparatus)  to  con- 
dense on  a  greater  number  of  nuclei,  be  they  relatively  large  like  the 
ions  or  small  like  the  colloidal  nuclei. 


CHAPTER  V. 

THE    COTEMPORANEOUS    VARIATIONS    OF   THE    NUCLEATION   AND  THE 
IONIZATION  OF  THE  ATMOSPHERE  OF  PROVIDENCE. 

By  Lui<u  B.  Josun. 

85.  Introduction. — The  results  obtained  by  Professor  Barus,*  showing 
a  characteristic  succession  of  the  values  of  atmospheric  nucleation 
throughout  the  year,  suggested  a  parallel  inquiry  into  the  variations  of 
the  number  of  ions  in  the  atmosphere  in  the  lapse  of  time.  The  present 
work  was  therefore  undertaken  at  his  instigation,  and  observations 
systematically  carried  forward  from  August,  1905,  to  April,  1906. 

In  addition  to  the  main  purpose  in  view,  it  was  hoped  that  a  number 
of  subsidiary  questions  might  be  answerable.  Thus  a  large  part  of  the 
nucleation  of  Providence  is  of  local  origin  and  enters  the  atmosphere 
with  other  products  of  combustion.  Initially  these  nuclei  were  either 
highly  ionized  themselves,  or  at  least  the  atmosphere  originally  received 
an  accession  of  ions  and  nuclei  in  proportional  quantities.  It  is  therefore 
of  interest  to  inquire  whether  any  of  the  ionization  survives,  or  whether 
there  is  any  connection  observable  between  corresponding  changes  of 
the  nucleation  and  the  ionization  of  a  given  place.  The  results,  which 
are  carefully  tabulated  in  the  present  paper,  seem  to  show  that  there  is 
no  such  connection  whatever;  or  that  the  persistent  ionization  arises 
from,  and  is  maintained  by,  causes  which  are  quite  distinct  from  the 
nucleation.  No  evidence  has  been  found  to  suggest  that  the  ionization 
is  either  emitted  or  absorbed  by  the  nucleation,  whence  it  follows  that 
the  ionization  arises  from  causes  wholly  non-local.  Apart  from  these 
main  purposes,  the  data  are  interesting  as  a  continuous  record  of  ion- 
ization (which  will  be  supplemented  in  the  future),  though,  as  yet,  suffi- 
cient time  has  not  elapsed  to  ascertain  whether  the  opposition  in  the 
monthly  positive  and  negative  ionizations  found  in  the  sequel  is  real 
or  incidental.     (Cf.  fig.  62.) 

Finally,  I  may  add  that  work  to  investigate  a  possible  relation  between 
the  nucleation  and  the  ionization  of  the  atmosphere  was  undertaken 
in  Helgoland  and  on  the  coast  of  the  Ostsee  by  Prof.  G.  Ludelingf  in  1902 
and  1903,  using  Aitken's  dust-counter.  The  time  during  which  obser- 
vations were  recorded  (August  21  to  September  16,  1902,  June  17  to 
July  4,  1903)  were  insufficient  to  warrant  general  conclusions,  however, 
apart  from  the  interesting  special  investigations  which  Professor  Ltide- 

*  Smithsonian  Contrib.,  xxxiv,  No.  1625,  chap,  ix,  1906;  Carnegie  Institution  pub- 
lication No.  40,  January,  1906,  chaps,  iv  and  v. 
fTwo  papers  in  the  Veroffentl.  Koniglich   Preussischen   Meteorologischen  Instituts, 

Berlin,  1904. 

123 


I24 


VAPOR    NUCLEI    AND    IONS. 


Fig.  570. — Disposition  of  coronal  apparatus  for  measuring  atmospheric  nucleation 
("dust").  V,  vacuum  chamber;  F,  fog  chamber;  G,  goniometer;  g,  gage;  e,  exhaus- 
tion pipe;  /,  support  for  trunnions.    Influx  pipe  at  left  end  of  fog  chamber. 


Fig.  576. — Disposition  of  apparatus  for  measuring  atmospheric  ionization.    E,  Ebert's 
apparatus;  B,  swiveled  brackets  sustaining  the  same;  T,  thermometers. 

ling's  paper  contains.  Reference  should  also  be  made  to  P.  Langevin's* 
important  discovery  of  slow-moving  ions  in  the  atmosphere  and  to  the 
work  of  M.  Bloch,f  but  comparisons  of  this  nature  are  quite  beyond  the 
scope  of  the  present  straightforward  experimental  research. 

86.  Measurements  of  nucleation. — Number  of  nuclei  in  the  atmosphere 
were  measured  by  aid  of  the  corona  of  cloudy  condensation,  in  the  way 

*P.  Langevin:  Bull.  Soc.  Franc,  de  Phys.,  p.  79,  1905. 

fBloch:  "Recherches  sur  la  conductibilite"  61ectrique,  etc.,"  Paris,  1904.     See  C.  T.  R. 
Wilson,  Trans.  Intern.  Congress,  St.  Louis,  vol.  1,  p.  365. 


ATMOSPHERIC    NUCLEI.  125 

fully  described  by  Professor  Barus  (loc.  cit.,  chap.  8),  and  the  same 
apparatus  (fig.  57  a)  which  had  proved  efficient  in  the  earlier  investi- 
gations was  used  throughout  the  present  experiments.  F  is  the  revolu- 
ble  wood  fog  chamber  with  plate-glass  windows,  V  the  vacuum  chamber, 
i  the  influx,  e  the  exhaustion  pipe,  g  the  gage,  G  the  goniometer.  Source 
of  light  beyond  F  is  not  shown.  Two  or  more  observations  were  usually 
made  daily,  together  with  the  meteorological  elements  of  wind,  weather, 
and  similar  data.  The  ionizations  referred  to  below,  section  91,  were 
taken  in  the  same  place. 

87.  Data  for  nucleation. — In  table  48  the  first  column  shows  the  day 
and  month,  the  second  the  time  in  hours  and  tenths  of  an  hour.  The 
third  gives  the  current  weather,  F  denoting  fair,  F'  partly  fair,  C  partly 
cloudy,  C  cloudy,  R  rain,  Sn  snow,  etc.  The  temperature  of  the  fog 
chamber.  (°C.)  and  the  temperature  of  the  atmosphere  (°F.)  follow. 
The  remaining  columns  show  the  data  referring  to  the  coronas,  the 
sixth  giving  the  diameters  (s)  of  the  coronas  at  the  end  of  a  radius 
of  30  cm.  Hence  5/30  is  nearly  their  angular  diameter  when  the 
eye  and  the  source  of  light  are  at  distances  85  cm.  and  250  cm.  on  oppo- 
site sides  of  the  fog  chamber.  The  seventh  column  indicates  the  colors 
of  the  successive  annuli  of  the  coronas,  reckoned  from  within  outward, 
w  denoting  white,  r  red,  o  orange,  y  yellow,  g  green,  b  blue,  p  purple,  etc. 
A  vertical  line  ( | )  shows  an  indeterminable  color,  a  prime  (0  an  ap- 
proach to  a  color,  etc.  The  last  column  gives  the  number  of  nuclei  in 
thousands  per  cubic  centimeter,  deduced  from  the  amount  of  water 
precipitated  per  cubic  centimeter,  and  the  sizes  of  particles  in  succes- 
sive coronas,  as  listed  by  Professor  Barus  (loc.  cit.). 

88.  Remarks  on  the  table  of  nucleation. — With  regard  to  the  individ- 
ual observations  very  little  can  be  adduced  that  has  not  already  ap- 
peared in  the  earlier  work.  Conformably  with  the  mild  winter,  the 
nucleation  as  a  whole  is  relatively  low,  an  unfortunate  occurrence  in  its 
bearing  on  the  purposes  of  the  present  work;  but  deductions  of  this 
character  will  be  brought  forward  with  advantage  in  connection  with 
the  daily  and  monthly  mean  nucleations  below.  It  is  rather  curious 
that  the  forest  fires  on  Cape  Cod  in  the  early  May  and  the  powder  com- 
bustion on  July  4  produce  so  little  impression;  on  the  other  hand,  the 
cold  weather  in  August  is  at  once  marked  by  large  coronas. 

89.  Mean  daily  nucleation. — The  data  of  table  48  have  been  averaged 
for  the  successive  days  in  table  49,  with  other  data  at  once  intelligible. 
The  results,  if  given  graphically  with  the  current  days  as  abscissas,  the 
corresponding  mean  nucleations  in  thousands  per  cubic  centimeter 
as  ordinates,  show  no  new  points  of  view.  One  may  note  the  rare 
occurrence  of  the  large  g-b-p  coronas  so  frequently  met  in  the  high 
nucleations  of  the  preceding  winter. 


126 


VAPOR    NUCLEI    AND    IONS. 


ATMOSPHERIC    NUCLEI. 


I27 


128 


VAPOR    NUCLEI    AND    IONS. 


ATMOSPHERIC    NUCLEI. 


129 


§        8        $        8 


i3o 


VAPOR    NUCLEI    AND    IONS. 


Table  48. — Showing  the  number  of  nuclei,  n,  per  cub.  cm.,  in  the  atmosphere 
at  the  times  (in  days  and  hours)  stated.  The  temperature  given  in  degrees  F. 
refers  to  the  atmosphere,  the  temperature  in  degrees  C.  to  the  fog  chamber. 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

»Xio-8. 

1905. 

Hours. 

May      4 

9-8 

C 

21 

50 

3-2 

cor 

"•3 

12.7 

C 

31 

53 

3 

2 

cor 

"•3 

6.2 

F 

21 

53 

3 

2 

cor 

"•3 

5 

9-4 

F 

20 

57 

4 

9 

wBP 

4i  -7 

6.0 

F 

20 

54 

4 

6 

cor 

34-8 

6 

9.6 

F 

20 

68 

5 

9 

wCg 

68 

12.7 

C 

21 

75 

6 

6 

wog 

90 

1. 1 

5 

8 

w  P  cor 

64- 5 

6.0 

c 

21 

68 

4 

•9 

wog 

4i  -7 

7 

9-7 

c 

21 

75 

4 

8 

wog 

39-5 

1-5 

c 

21 

84 

4 

8 

wog 

39-5 

6.8 

F 

22 

73 

3 

8 

cor 

19 

8 

9.0 

F 

21 

60 

6 

7 

wog 

92.5 

9-5 

F 

21 

65 

7 

1 

wyg 

100 

30 

F 

21 

65 

4 

8 

wrg 

39-5 

9 

9.8 

R 

20 

61 

4 

8 

wrg 

39-5 

1.4 

F 

21 

65 

4 

9 

wB  P 

41.7 

6.3 

F 

20 

59 

4 

6 

wog 

34-8 

10 

9.6 

F 

19 

60 

5 

6 

wog 

58.7 

33 

F 

19 

68 

4 

7 

wog 

37-2 

6.2 

F 

66 

4 

7 

37-2 

11 

9-3 

F 

T9 

66 

5 

6 

WCg 

58.7 

6.2 

F 

20 

65 

4 

5 

wrg 

32.4 

12 

3-2 

C 

20 

68 

3 

8 

cor 

19 

6.0 

C 

66 

4 

7 

37-2 

13 

9-4 

C 

60 

4 

6 

34-8 

2.8 

C 

i8 

62 

3 

6 

cor 

16.2 

6.3 

C 

55 

3 

2 

cor 

"•3 

14 

9.8 

C 

19 

59 

3 

3 

cor 

12.5 

1.4 

R 

19 

49 

3 

8 

cor 

19 

6.2 

R' 

19 

61 

3 

8 

cor 

19 

15 

9-i 

C 

19 

60 

4 

5 

wig 

32.4 

3-8 

C 

19 

67 

3 

6 

wrg 

16.2 

6-3 

C 

19 

61 

3 

6 

wrg 

16.2 

16 

93 

C 

18 

55 

3 

5 

wrg 

15 

3-4 

R' 

18 

52 

3 

1 

wrg 

10.2 

17 

93 

C 

18 

49 

3 

6 

cor 

16.2 

6.0 

c 

17 

49 

3 

9 

cor 

20.5 

18 

9-4 

c 

16 

55 

3 

7 

cor 

17-5 

2.8 

F 

18 

65 

4 

6 

gBP 

34-8 

50 

F 

18 

64 

19 

10. 0 

C 

18 

65 

4 

5 

wrg 

32.4 

6.0 

C 

18 

66 

4 

6 

wrg 

34-8 

20 

10.3 

F 

17 

57 

6 

0 

WCg 

70.5 

6-3 

F 

18 

58 

3 

9 

cor 

20.5 

21 

9-4 

F 

18 

59 

4 

6 

gBP 

34-8 

3-2 

F 

18 

65 

3 

5 

cor 

15 

22 

9-i 

F 

17 

64 

4 

7 

cor 

37-2 

3-7 

F 

18 

69 

4 

6 

cor 

34-8 

23 

9.0 

C 

18 

60 

5 

2 

wP  cor 

48.2 

6.5 

F 

18 

59 

4 

6 

wrg 

34-8 

24 

9-3 

F 

17 

59 

6 

1 

wrg 

73-3 

6-7 

F 

17 

60 

4 

1 

cor 

24 

25 

9-3 

F 

17 

65 

6 

2 

wrg 

76.5 

ATMOSPHERIC    NUCLEI. 

Table  48. — Continued. 


131 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

wxio-3. 

1905. 

Hours. 

May     25 

3-3 

F 

18 

69 

4-8 

wBP 

39-5 

26 

9.2 

F 

18 

72 

4 

S 

wog 

395 

6.0 

F 

19 

69 

4 

3 

cor 

28 

27 

8.8 

C 

19 

69 

3 

8 

cor 

19 

6.7 

R' 

20 

67 

3 

6 

cor 

16.2 

28 

9.8 

F 

20 

77 

4 

3 

wrg 

28 

5-o 

F 

20 

75 

4 

7 

wrg 

37-2 

29 

9.4 

F 

20 

74 

3 

9 

wrg 

20.5 

30 

9.4 

C 

21 

63 

3 

4 

cor 

13-8 

3-3 

F 

21 

70 

3 

4 

cor 

138 

3i 

9.0 

F 

20 

64 

3 

2 

cor 

"•3 

June      1 

9.2 

C 

18 

60 

3 

5 

cor 

15 

4.0 

F 

19 

64 

3 

5 

cor 

15 

2 

9-9 

F 

19 

65 

4 

7 

cor 

37-2 

3 

6.0 

F 

19 

69 

4 

3 

cor 

28 

4 

9-5 

F 

19 

70 

4 

8 

w  Pcor 

39-5 

5-o 

F 

19 

7i 

3 

7 

cor 

17-5 

5 

9-3 

F 

20 

73 

3 

7 

cor 

17.5 

6 

9-9 

R 

21 

63 

2 

9 

cor 

8-3 

7 

9-7 

C 

18 

58 

4 

6 

cor 

34-8 

8 

9.2 

R' 

18 

5o 

4 

1 

cor 

24 

6.4 

F 

18 

55 

4 

1 

cor 

24 

9 

9.4 

F 

17 

66 

5 

4 

w  B  cor 

54-2 

5-8 

F 

19 

69 

4 

0 

cor 

22 

10 

9.2 

F 

19 

73 

5 

2 

w 

48.2 

6.1 

F 

20 

75 

4 

0 

cor 

22 

11 

"3 

F 

19 

7i 

3 

9 

cor 

20.5 

6.0 

C 

19 

66 

3 

4 

cor 

13.8 

12 

9-5 

R 

19 

65 

4 

7 

cor 

37.2 

5-5 

R 

19 

62 

3 

9 

cor 

20.5 

13 

9-5 

C 

20 

69 

4 

4 

wrg 

30 

14 

9.6 

F 

20 

73 

4 

4 

wrg 

30 

15 

9.6 

F 

21 

81 

5 

7 

wrg 

61.5 

6.0 

F 

22 

76 

3 

s 

cor 

19 

16 

9-7 

F 

22 

79 

4 

6 

cor 

34-8 

5-6 

F 

23 

78 

4 

3 

cor 

28 

17 

9-5 

F 

22 

73 

4 

2 

cor 

25.8 

18 

10.9 

F 

23 

86 

5 

0 

cor 

43-8 

5-4 

F 

24 

84 

3 

1 

cor 

10.  2 

19 

10.8 

F 

20 

62 

2 

s 

cor 

7-3 

20 

12.4 

R 

18 

58 

3 

3 

cor 

12.5 

22 

10.4 

C 

20 

69 

4 

1 

cor 

24 

23 

10.2 

F 

21 

82 

3 

0 

cor 

9-3 

24 

10. 0 

C 

21 

74 

4 

s 

wBP 

395 

6.0 

F 

21 

76 

4 

2 

cor 

25.8 

25 

11. 4 

F 

21 

82 

3 

7 

cor 

17.5 

26 

10.5 

F 

23 

82 

3 

9 

cor 

20.5 

27 

10. 0 

F' 

21 

67 

4 

4 

wr 

30.0 

28 

11 .0 

F 

20 

70 

4 

s 

gbP 

39-5 

6.0 

F 

21 

7i 

3 

9 

cor 

20.5 

29 

10.3 

F 

21 

76 

4 

s 

w  ocor 

39-5 

6.6 

F 

21 

77 

3 

6 

cor 

16.2 

.       30 

10.9 

F 

21 

80 

4 

6 

w  y' 

34-8 

July      1 

10.6 

F 

22 

76 

4- 

1 

cor 

24 

6.0 

F 

73 

4- 

6 

cor 

34-8 

132 


VAPOR    NUCLEI    AND    IONS. 
Table  48. — Continued. 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

n  X  io-3. 

1905. 

Hours. 

July       2 

12.0 

R' 

23 

72 

3-8 

cor 

19 

a 

«*3 

C 

22 

77 

3- 

5 

cor 

15 

4 

11 .2 

F 

23 

86 

4- 

7 

w  0 

37-2 

6.5 

F 

23 

81 

3- 

1 

cor 

10.  2 

5 

10.8 

F 

23 

73 

3 

2 

cor 

"•3 

6 

9.8 

C 

23 

72 

2 

9 

cor 

8-3 

5-5 

F 

23 

72 

3 

9 

cor 

20.5 

7 

10.7 

C 

23 

79 

5 

9 

wcg 

68 

8 

12.0 

c 

23 

82 

4 

6 

wrg 

34-8 

4.0 

F 

80 

4 

2 

wcg 

25.8 

9 

11 .0 

F 

24 

85 

4 

6 

gbp 

34-8 

6.0 

F 

24 

84 

2 

4 

cor 

4.6 

1 1 

10.3 

F 

26 

85 

4 

7 

wrg' 

37-2 

4-5 

e 

26 

88 

4 

1 

cor 

24 

12 

10.6 

F 

26 

89 

5 

4 

w  P  cor 

54-2 

6.0 

F 

27 

85 

3 

7 

cor 

17-5 

13 

11 .0 

e 

26 

88 

4 

9 

w  B  cor 

41.7 

5-7 

F 

84 

3 

7 

cor 

17-5 

14 

10. 0 

F 

26 

84 

4 

7 

gBP 

37-2 

5-5 

F 

27 

83 

4 

4 

w  r 

30 

15 

10.4 

F 

26 

82 

4 

0 

cor 

22 

F 

26 

3 

1 

cor 

10.  2 

16 

10.7 

F 

25 

78 

3 

8 

wr 

19 

17 

12.5 

R' 

26 

85 

3 

5 

cor 

15 

5-3 

R' 

26 

90 

4 

1 

wrg 

24 

18 

10.7 

F 

26 

9i 

4 

7 

37-2 

19 

10.7 

F 

27 

92 

4 

1 

cor 

24 

6.0 

R 

28 

84 

4 

1 

cor 

24 

20 

10.5 

F 

27 

86 

4 

2 

cor 

25.8 

6.0 

F 

27 

82 

3 

3 

cor 

12.5 

21 

10.6 

F 

26 

77 

4 

3 

w  0 

28 

6.0 

F 

26 

79 

3 

0 

cor 

9-3 

22 

10.5 

F 

25 

80 

5 

5 

wcg 

56.2 

6.0 

C 

73 

3 

0 

cor 

9-3 

23 

10.3 

R 

25 

65 

2 

2 

cor 

3-3 

6-5 

C 

67 

1 

8 

cor 

1.9 

24 

10.3 

C 

23 

73 

4 

0 

cor 

22 

25 

10.  2 

C 

23 

77 

4 

5 

w  0  cor 

32.4 

6.0 

F 

23 

77 

3 

7 

cor 

17-5 

27 

10.5 

F 

22 

80 

4 

2 

wrg 

25.8 

4-7 

F 

23 

81 

4 

6 

wrg 

34-8 

29 

9.8 

C 

23 

76 

2 

6 

cor 

5-9 

4.6 

R 

24 

73 

3 

5 

wrg 

15 

30 

10.6 

R 

75 

2 

2 

cor 

3-3 

6.0 

R' 

24 

70 

2 

4 

cor 

4.6 

3i 

10.3 

C 

23 

66 

2 

7 

cor 

6.6 

4-3 

C 

23 

67 

2 

8 

cor 

7-3 

Aug.      1 

10.4 

R 

22 

63 

3 

.  2 

cor 

11. 3 

6.0 

R 

21 

65 

3 

2 

cor 

11. 3 

2 

10. 0 

F 

21 

76 

4 

6 

wrg 

34-8 

6.0 

C 

22 

75 

3 

6 

cor 

16.2 

3 

9.6 

F 

21 

75 

5 

6 

wcg 

58.7 

12.7 

F 

21 

81 

5 

.  2 

w  P  cor 

48.2 

5-i 

F 

76 

4 

.  1 

cor 

24 

4 

9-7 

F 

21 

78 

4 

-5 

gBP 

32.4 

ATMOSPHERIC    NUCLEI. 
Table  48. — Continued. 


133 


Date. 

Time. 

Weather. 

CC. 

°F. 

s. 

Corona. 

n  X  io~8. 

1905. 

Hours. 

Aug.      4 

5-5 

F 

22 

75 

4-3 

cor 

28 

5 

9-7 

C 

23 

77 

3 

7 

cor 

17-5 

6.0 

F 

23 

73 

3 

4 

cor 

13-8 

6 

10.7 

F 

23 

80 

4 

0 

cor 

22 

6.0 

F 

23 

76 

3 

2 

cor 

17-5 

7 

9.4 

F 

23 

82 

4 

6 

wrg 

34-8 

R' 

24 

79 

3 

9 

20.5 

8 

10. 0 

R' 

24 

77 

4 

3 

wrg 

28 

6.0 

C 

25 

80 

3 

9 

20.5 

9 

9.6 

c 

24 

76 

3 

6 

16.2 

6.4 

R 

25 

73 

4 

3 

wrg 

28 

10 

9.6 

F 

24 

81 

4 

6 

gBP 

34-8 

6.0 

C 

79 

4 

6 

wrg 

34-8 

11 

9.8 

C 

25 

80 

4 

7 

w  0  cor 

37-2 

6.0 

F 

27 

80 

3 

6 

cor 

16.2 

12 

10.5 

C 

26 

85 

4 

6 

gBP 

34-8 

6.0 

c 

26 

79 

3 

3 

cor 

12.5 

13 

10.7 

c 

26 

86 

2 

2 

cor 

3-3 

6.0 

c 

26 

78 

3 

2 

cor 

11. 3 

14 

9-7 

F 

25 

72 

3 

5 

cor 

15 

15 

10.7 

R 

23 

66 

3 

5 

cor 

i5 

6-3 

R' 

23 

60 

2 

3 

cor 

4 

16 

11. 6 

R' 

21 

60 

2 

9 

cor 

8-3 

17 

10.5 

F 

20 

70 

6 

5 

wog 

86.5 

12.5 

F 

20 

74 

4 

9 

g'BP 

41.7 

6-5 

F 

20 

66 

3 

6 

cor 

16.2 

18 

10.4 

F 

20 

70 

4 

4 

wrg 

30 

19 

9.8 

F 

20 

68 

2 

7 

cor 

6.6 

20 

11 .0 

F 

19 

69 

4 

0 

cor 

22 

21 

10.5 

F 

20 

77 

4 

0 

cor 

22 

22 

10.3 

F 

22 

83 

4 

6 

gBP 

34-8 

6.2 

C 

23 

80 

3 

9 

20.5 

23 

10.4 

F 

22 

82 

3 

8 

19 

24 

10.7 

F 

23 

85 

4 

7 

wog 

37-2 

6.0 

R 

25 

79 

4 

6 

gBP 

34-8 

25 

10.4 

R' 

23 

66 

2 

8 

cor 

7-3 

6.0 

C 

67 

3 

5 

wrg 

15 

26 

10.7 

F 

22 

70 

3 

4 

wrg 

13-8 

6.0 

F 

22 

68 

2 

5 

cor 

5-2 

27 

10. 1 

R' 

21 

60 

2 

4 

cor 

4.6 

6-5 

C 

21 

59 

2 

7 

cor 

6.6 

28 

9.8 

F 

19 

65 

4 

5 

gBP 

32.4 

6.0 

F 

20 

65 

4 

7 

wrg 

37-2 

29 

10. 0 

F 

20 

72 

3 

7 

cor 

17-5 

30 

F 

20 

75 

3 

2 

cor 

"•3 

30 

10.8 

C 

20 

73 

3 

9 

cor 

20.5 

3-7 

R 

21 

74 

4 

4 

wrg 

30 

3i 

10. 0 

R 

20 

64 

3 

1 

cor 

10.  2 

3-o 

C 

20 

69 

2 

5 

cor 

5-2 

Sept.      1 

10.6 

c 

20 

69 

4 

4 

wrg 

30 

3-o 

R 

20 

67 

3 

7 

cor 

17-5 

2 

9-7 

e 

20 

70 

2 

6 

cor 

5-9 

i-5 

c 

20 

70 

3 

5 

wgrp 

15 

4 

10.5 

5, 

21 

69 

2 

5 

cor 

5.2 

17 

R' 

21 

72 

2 

0 

cor 

2-5 

134 


VAPOR    NUCLEI    AND    IONS. 
Table  48. — Continued. 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

n  X  io-3. 

1905- 

Hours. 

Sept.      7 

10.3 

F 

20 

71 

3-6 

cor 

16.2 

3-3 

C 

20 

71 

3 

•7 

cor 

17-5 

8 

10.2 

F 

20 

70 

4 

•3 

wrg 

28 

2-5 

F 

20 

74 

3 

.  1 

cor 

10.  2 

9 

9-7 

F 

20 

74 

4 

.8 

wrg 

39-5 

2-5 

F 

20 

78 

4 

.0 

wrg 

22 

11 

9-9 

F 

21 

72 

4 

.2 

cor 

25.8 

2-5 

C 

21 

7i 

3 

.8 

cor 

19 

12 

10.2 

R 

20 

63 

3 

.  1 

cor 

10.  2 

2-7 

R 

21 

66 

3 

.8 

cor 

19 

13 

10.3 

C 

20 

70 

3 

•3 

cor 

12.5 

2.4 

C 

20 

74 

3 

8 

cor 

19 

14 

10.4 

F 

18 

57 

4 

.2 

cor 

25.8 

2-5 

F 

18 

62 

4 

5 

ygp 

32.4 

15 

10.4 

F 

15 

62 

5 

0 

wrg 

43-8 

2-5 

F 

17 

64 

3 

8 

cor 

19.0 

16 

10.5 

C 

17 

62 

3 

6 

cor 

16.2 

2.0 

C 

18 

64 

3 

7 

cor 

17-5 

18 

10. 0 

C 

18 

68 

3 

6 

cor 

16.  2 

3-6 

C 

19 

7i 

3 

8 

cor 

19 

19 

9-8 

R 

19 

68 

3 

4 

cor 

13.8 

3-3 

C 

19 

69 

2 

9 

cor 

8-3 

20 

10.3 

c 

19 

67 

3 

5 

cor 

15 

3-7 

c 

20 

69 

3 

8 

cor 

19 

21 

8-7 

F 

19 

67 

3 

8 

cor 

19 

3-4 

F 

19 

74 

3 

9 

cor 

20.5 

22 

9.8 

F 

19 

70 

4 

7 

ygp 

37-2 

5-o 

F 

21 

75 

4 

5 

ygp 

32-4 

23 

9.0 

F 

19 

67 

4 

2 

cor 

25.8 

25 

11. 0 

F 

18 

61 

4 

4 

cor 

30 

2.7 

F 

18 

62 

3 

9 

cor 

20.5 

26 

90 

F 

17 

50 

5 

4 

wrg 

54-2 

3-7 

F 

17 

58 

4 

7 

cor 

37-2 

27 

O.o 

F 

16 

52 

5 

1 

wrg 

46 

5-5 

F 

16 

60 

5 

6 

wrg 

58.7 

28 

9-5 

F 

16 

65 

4 

6 

ygp 

34-8 

3-5 

F 

18 

74 

3 

5 

cor 

15 

29 

9.2 

F 

17 

63 

5 

5 

wrg 

56.2 

25 

F 

18 

69 

4 

1 

cor 

24.0 

30 

9.0 

F 

18 

63 

4 

4 

ygp 

30 

3-3 

F 

20 

7i 

4 

2 

cor 

25.8 

Oct.       2 

9.2 

C 

18 

62 

4 

5 

cor 

32-4 

2.7 

C 

18 

65 

3 

8 

cor 

19 

3 

10. 0 

F 

19 

72 

3 

4 

cor 

13-8 

2.8 

F 

19 

75 

3 

8 

cor 

19 

4 

9.8 

F 

18 

7i 

4 

9 

cor 

41.7 

2.9 

F 

10 

76 

4 

3 

cor 

28 

5 

10.5 

F 

19 

76 

4- 

9 

ygp 

41.7 

6 

9-3 

F 

18 

58 

4- 

7 

ygp 

37-2 

3-i 

F 

18 

63 

4- 

6 

cor 

34-8 

7 

9-i 

F 

17 

56 

5- 

2 

cor 

48.2 

2.6 

F 

17 

63 

4- 

8 

cor 

39-5 

9 

12. 1 

F 

18 

74 

5- 

4 

wrg 

54-2 

4-5 

F 

18 

7i 

4- 

7 

cor 

37-2 

10 

9-9 

F 

16 

58 

3- 

7 

cor 

17-5 

ATMOSPHERIC    NUCLEI. 

Table  48. — Continued. 


135 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

n  X  10-8. 

1905. 

Hours. 

Oct.     10 

2.5 

F 

17 

64 

4-4 

wrg 

30 

11 

9.8 

C 

16 

56 

4 

5 

wrg 

324 

2.2 

C 

16 

58 

4 

7 

wrg 

37 

2 

12 

9.0 

F 

16 

54 

4 

3 

wrg 

28 

2.7 

F 

17 

59 

4 

5 

wrg 

32 

4 

13 

11. 0 

F 

16 

56 

4 

7 

ygp 

37 

2 

2.6 

C 

16 

58 

4 

8 

ygp 

39 

5 

H 

10. 0 

F 

17 

61 

4 

8 

ygp 

39 

5 

2.6 

F 

18 

68 

5 

0 

ygp 

43 

8 

16 

2-5 

F 

20 

75 

4 

8 

ygp 

39 

5 

4-7 

F 

20 

73 

5 

2 

w  B  cor 

48 

2 

17 

10.3 

F 

18 

60 

5 

7 

wrg 

61 

5 

2.7 

F 

18 

63 

5 

0 

wrg 

43 

8 

18 

9.2 

F 

18 

61 

4 

5 

cor 

32 

4 

2.7 

F 

18 

66 

4 

6 

cor 

34 

8 

19 

12.0 

C 

19 

75 

4 

2 

cor 

25 

8 

3-5 

C 

20 

72 

4 

6 

g  P  cor 

34 

8 

20 

11. 6 

R 

19 

60 

3 

7 

cor 

17 

5 

2.6 

R 

18 

60 

3 

7 

cor 

17 

5 

23 

12.  2 

F 

17 

52 

4 

7 

gB 

37 

2 

4-3 

F 

17 

52 

4 

7 

gB 

37 

2 

24 

10.2 

F 

16 

54 

4 

7 

cor 

37 

2 

2.7 

F 

17 

61 

4 

7 

ygp 

37 

2 

25 

12. 1 

F 

17 

55 

4 

7 

wrg 

37 

2 

4.1 

C 

18 

54 

4 

5 

wB 

32 

4 

26 

2-7 

C 

18 

46 

4 

6 

wrg 

34 

8 

4.6 

F 

18 

43 

4 

0 

Bg 

22 

27 

11. 0 

F 

17 

50 

5 

4 

gBP 

54 

2 

2.8 

F 

18 

53 

4 

8 

ygB 

39 

5 

30 

2.7 

F 

18 

52 

4 

7 

ygB 

37 

2 

4-3 

F 

18 

47 

4 

6 

wrg 

34 

8 

3i 

"•5 

C 

18 

54 

4 

s 

wBrg 

39 

5 

3-7 

C 

19 

54 

4 

5 

wrg 

32 

4 

Nov.      1 

3-o 

F 

18 

64 

4 

8 

gBP 

39 

5 

5-6 

F 

19 

54 

4 

7 

wBr  B 

37 

2 

3 

3-7 

C 

18 

50 

4 

4 

wrg 

30 

5-o 

C 

18 

48 

4 

6 

wrg 

34 

8 

4 

10.2 

F 

18 

S3 

4 

7 

wrg 

37 

2 

2.4 

F 

17 

52 

4 

0 

wBr  B 

22 

6 

2-7 

R 

17 

5i 

4 

3 

wrg 

28 

7 

10.5 

F 

18 

48 

5 

7 

wrg 

61.5 

3-o 

C 

18 

48 

3 

7 

wBrB 

17-5 

8 

3-o 

C 

19 

48 

4 

7 

w  Br  B 

37-2 

9 

2.6 

C 

19 

45 

4 

8 

wBrB 

39-5 

10 

11 . 1 

F 

21 

46 

5 

3 

gBP 

50.5 

3-2 

C 

20 

45 

5 

0 

wBzB 

43-8 

1 1 

9.5 

F 

20 

40 

6 

2 

wrg 

76.5 

10.5 

F 

20 

42 

6 

8 

yg 

95 

12 

2.5 

F 

21 

49 

5 

4 

gBP 

54-2 

13 

3.2 

F 

23 

56 

5 

3 

gBP 

505 

14 

10.7 

F 

20 

28 

6 

6 

yg 

90 

16 

2.5 

C 

20 

5i 

4 

9 

wBr  B 

41.7 

17 

II. 2 

F 

19 

44 

4 

5 

cor 

32.4 

2.7 

F 

19 

45 

4 

5 

weg 

32.4 

18 

9-8 

F 

21 

44 

4 

7 

yg 

37-2 

136 


VAPOR    NUCLEI    AND    IONS. 
Table  48. — Continued. 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

n  X  to-3. 

1905. 

Hours. 

Nov.    20 

2-7 

F 

20 

38 

4.8 

w  Br  B 

39-5 

21 

10.6 

F 

20 

46 

6 

•5 

yg 

86.5 

3-3 

F 

21 

52 

6 

.0 

wrg 

70.5 

22 

12. 1 

F 

20 

52 

6 

.  1 

wrg 

73-3 

4.0 

C 

20 

52 

6 

.  1 

wrg 

73-3 

23 

2.7 

F 

22 

59 

4 

.8 

wBr  B 

39-5 

24 

2-5 

F 

22 

63 

4 

.8 

wBr  B 

39-5 

5-3 

F 

22 

55 

4 

•7 

wBr  B 

37-2 

27 

3-5 

I 

18 

45 

4 

.8 

w  Br  B 

39-5 

5-o 

F 

18 

42 

4 

.6 

wBr  B 

34-8 

28 

10.4 

C 

19 

38 

4 

•7 

wB  g 

37-2 

3-o 

C 

19 

37 

4 

.8 

wBg 

39-5 

Dec.      4 

12. 1 

F 

21 

39 

4 

.2 

cor 

25.8 

2-7 

F 

20 

37 

4 

•3 

wBr  B 

28 

5 

11 .0 

F 

20 

30 

5 

7 

wrg 

61.5 

2-7 

F 

19 

36 

5 

•4 

w  Br  B 

54-2 

6 

12  2 

C 

20 

40 

5 

.6 

wrg 

58.7 

3-o 

C 

20 

40 

4 

.6 

wBg 

34-8 

7 

2.7 

F 

19 

46 

4 

.8 

wBg 

39-5 

8 

11 . 2 

F 

22 

50 

4 

•9 

wBr  B 

41.7 

3-2 

F 

22 

53 

5 

•4 

wBr  B 

54-2 

9 

10.7 

C 

22 

42 

3 

•9 

cor 

20.5 

11 

30 

C 

20 

34 

5 

.6 

wrg 

58.7 

12 

10.7 

C 

21 

28 

4 

.  -7 

wBr  B 

37-2 

2.7 

F 

20 

35 

5 

.O 

wgB 

43-? 

13 

12.  2 

F 

22 

44 

6 

.  I 

wrg 

73-3 

3-5 

F 

22 

45 

5 

•7 

wgB 

61.5 

H 

3-7 

F 

22 

34 

5 

.8 

WgP 

64- 5 

x5 

11 . 1 

C 

22 

22 

6 

5 

y  g 

86.5 

16 

3-5 

C 

21 

32 

5 

0 

WgP 

43-8 

18 

4.0 

F 

23 

46 

6 

•7 

gbP 

92.5 

19 

10.5 

F 

23 

42 

4 

7 

w  Br  g 

37-2 

2-5 

C 

23 

46 

4 

7 

w  Br  g 

37-2 

20 

10.6 

F 

23 

45 

5 

2 

gbP 

48.2 

3-9 

F 

23 

47 

4 

8 

w  Br  g 

39-5 

21 

10.7 

R 

23 

46 

3 

S 

cor 

19 

3-i 

R' 

23 

52 

4 

9 

WgP 

41.7 

1906. 

Jan.       1 

3-7 

F 

23 

36 

4 

6 

wrg 

32-4 

2 

10.7 

F 

22 

3i 

5 

7 

wrg 

61.5 

3-5 

C 

21 

36 

5 

6 

wB  P 

58.7 

3 

11. 7 

F 

20 

32 

4 

7 

gBP 

37-2 

3-4 

C 

20 

34 

1 

8 

w  Br  g 

39-5 

4 

1.0 

R' 

22 

58 

5 

0 

gBP 

43-8 

3-2 

C 

22 

57 

6 

2 

wrg 

76.5 

5 

10. 0 

F 

23 

43 

6 

0 

wrg 

70.5 

2.7 

F 

22 

44 

5 

3 

wBr  P 

50.5 

6 

10.6 

C 

21 

38 

5 

9 

wrg 

68 

4-3 

F 

20 

37 

5 

9 

wrg 

68 

8 

12.5 

C 

19 

27 

4 

7 

w  Br  g 

37-2 

4-5 

Sn 

20 

26 

4 

7 

w  Br  g 

37.2 

9 

n. 0 

F 

20 

20 

6 

7 

yg 

92.5 

30 

F 

19 

26 

6. 

5 

yg 

86.5 

10 

4.0 

F 

18 

25 

6. 

4 

wrg 

83-5 

11 

12.  2 

F 

19 

32 

5- 

9 

wrg 

68 

50 

F 

19 

3i 

6. 

4 

wrg 

83.5 

12 

11 . 2 

F 

22 

5i 

5- 

9 

wrg 

68 

ATMOSPHERIC    NUCLEI. 
Table  48. — Continued. 


137 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

n  X  io-'. 

1906. 

Hours. 

Jan.     1 2 

4.8 

F 

22 

47 

5-6 

wrg 

58.7 

13 

10.5 

F 

21 

38 

4 

5 

cor 

32.4 

3-3 

C 

21 

36 

3 

8 

wBrP 

19 

15 

10. 0 

F 

21 

3i 

4 

9 

wBrP 

41.7 

16 

"•5 

R' 

20 

49 

4 

8 

wrg 

39-5 

3-5 

R' 

22 

49 

5 

5 

gBP 

56.2 

17 

10. 1 

F 

20 

39 

6 

0 

wrg 

70.5 

3-5 

F 

18 

40 

4 

7 

wBr  B 

372 

18 

12.3 

R' 

18 

44 

4 

9 

gPr 

41-7 

4.8 

C 

19 

43 

5 

1 

wBrP 

46 

19 

10. 0 

F 

19 

39 

4 

6 

w  Br  g 

34-8 

2-7 

F 

20 

4i 

5 

8 

wBr  P 

645 

20 

10.4 

C 

20 

35 

4 

8 

gBr 

39-5 

3-2 

R' 

20 

40 

4 

9 

gBr 

41.7 

22 

12.5 

C 

23 

53 

4 

5 

w  Br  g 

32.4 

4.0 

F 

22 

5i 

4 

7 

w  Br  g 

37-2 

23 

10.3 

F 

22 

63 

5 

0 

wBrP 

43-8 

5-0 

F 

23 

63 

5 

1 

wBrP 

46 

24 

10. 1 

F 

20 

43 

6 

5 

yg 

86.5 

25 

9.8 

F 

20 

26 

5 

3 

wBr  P 

50.5 

3-2 

F 

19 

26 

4 

5 

wBrP 

32 -4 

26 

10. 0 

F 

19 

29 

4 

8 

w  Br  g 

39-5 

3-3 

F 

19 

39 

4 

5 

wBrg 

32-4 

27 

10.  2 

F 

20 

37 

6 

3 

yG 

80.5 

4.4 

F 

20 

46 

4 

9 

wBrP 

41.7 

29 

12.0 

F 

20 

29 

6 

S 

yG 

95 

3-7 

F 

20 

33 

4 

9 

gPr 

41.7 

30 

10.5 

F 

20 

4i 

6 

1 

wrg 

73-3 

3-0 

F 

20 

49 

5 

1 

wBrB 

46 

3i 

12.3 

F 

21 

52 

4 

7 

w  Br  g 

37-2 

3-3 

F 

21 

49 

4 

5 

w  Br  g 

32-4 

Feb.       1 

12.2 

F 

21 

43 

6 

O 

Grg 

705 

50 

F 

21 

43 

5 

1 

wBr  P 

46 

2 

11. 0 

F 

19 

20 

6 

5 

yG 

86.5 

50 

F 

17 

14 

5 

5 

wr  b  og 

56.2 

3 

10.  2 

F 

18 

9 

6 

2 

wrg 

76.5 

6.2 

F 

18 

19 

6 

1 

wrg 

73-3 

4 

10. 1 

F 

20 

35 

5 

0 

w  P  cor 

43-8 

12.5 

F 

20 

39 

5 

2 

w  P  cor 

48.2 

6.3 

F 

21 

37 

4 

6 

cor 

34-8 

5 

50 

22 

39 

4 

7 

cor 

37-2 

6 

9-5 

F 

21 

20 

6 

s 

gBP 

95 

"•3 

F 

21 

21 

6 

A 

wrg 

83.5 

3-5 

F 

21 

23 

5 

2 

cor 

48.2 

7 

10.5 

Sn' 

19 

15 

6 

0 

wrg 

70.5 

12. 1 

Sn' 

18 

18 

6 

7 

w  0  b  g 

925 

3-6 

F 

19 

24 

6 

0 

wrg 

70.5 

6.1 

19 

22 

5 

9 

wrg 

68 

8 

9-5 

F 

20 

19 

5 

9 

wrg 

68 

11. 7 

F 

20 

29 

4 

s 

gB' 

39-5 

3-o 

F 

19 

34 

4 

8 

wrg 

39-5 

5-6 

F 

19 

3i 

5 

8 

wrg 

64-5 

9 

11.  2 

R 

21 

38 

4 

6 

wrg 

34-8 

4.8 

C 

21 

35 

4 

8 

wPcor 

39-5 

10 

9-7 

F 

22 

32 

4 

8 

gBP 

39-5 

12.8 

F 

21 

36 

4 

8 

gBP 

39-5 

5-2 

F 

22 

35 

4 

8 

gBP 

39-5 

138 


VAPOR    NUCLEI    AND    IONS. 
Table  48. — Continued. 


Date. 

Time. 

Weather. 

°C. 

°F. 

s. 

Corona. 

wxio-3. 

1906. 

Hours. 

Feb.     1 1 

9.8 

F 

22 

22 

6-5 

yobg 

86.5 

12  .0 

F 

27 

6 

.0 

wrg 

70 

5 

5-o 

F 

22 

28 

4 

.8 

w  r  0  g 

39 

5 

12 

9.6 

F 

22 

34 

5 

•3 

wrg 

50 

5 

1.5 

F 

21 

41 

4 

.8 

cor 

39 

5 

3-5 

C 

20 

40 

4 

•4 

cor 

30 

13 

12.2 

R 

22 

42 

4 

.6 

gBP 

34 

8 

6.0 

C 

23 

40 

4 

.6 

cor 

34 

8 

14 

12.3 

C 

23 

47 

3 

•9 

cor 

20 

5 

4.1 

c 

23 

48 

4 

.  2 

cor 

25 

8 

15 

1 .0 

c 

20 

24 

6 

.8 

gBP 

95 

5-i 

F 

21 

25 

5 

.  1 

gBr 

46 

16 

12.3 

F 

20 

26 

6 

•5 

yg 

86.5 

50 

F 

21 

34 

5 

•4 

wrobg 

54 

2 

17 

12.3 

F 

21 

30 

4 

•7 

w  Br  g 

37 

2 

4.0 

F 

21 

40 

4 

.8 

gBr 

39 

5 

19 

12.3 

F 

22 

44 

5 

.0 

yg 

43 

8 

50 

C 

22 

43 

5 

.6 

wBr  P 

58 

7 

20 

n-3 

F 

22 

42 

5 

.8 

wBr  P 

64 

5 

4-7 

F 

22 

47 

5 

.0 

wBr  P 

43 

8 

21 

5-i 

R 

23 

54 

4 

•7 

gBP 

37 

2 

22 

11 .0 

F 

24 

5i 

5 

.8 

wrg 

64 

5 

23 

50 

F 

22 

45 

4 

•7 

w  Br  g 

37 

2 

26 

4-3 

F 

21 

45 

4 

•9 

w  Br  g 

4i 

7 

27 

11.  S 

F 

20 

35 

6 

.  2 

yg 

76 

5 

5-o 

F 

19 

33 

4 

•9 

gBr 

4i 

7 

28 

12.2 

F 

18 

21 

6 

■7 

yg 

92 

5 

5-o 

F 

18 

22 

5 

•9 

wrg 

68 

March    1 

12.5 

F 

17 

27 

6 

•7 

yg 

92 

5 

5-o 

F 

18 

32 

5 

•7 

wrg 

61 

5 

2 

n-5 

F 

19 

36 

6 

•4 

yg 

83 

5 

5-7 

F 

20 

40 

5 

6 

wrg 

58 

7 

3 

10.7 

R' 

21 

36 

4 

•5 

cor 

32 

4 

5 

12.5 

F 

22 

44 

4 

8 

wbP 

39 

5 

4-7 

F 

22 

45 

4 

8 

wgpr 

39 

5 

6 

11. 7 

F 

21 

36 

5 

0 

w  b  p 

43 

8 

5-o 

F 

21 

38 

5 

9 

wrg 

68 

7 

12.5 

C 

20 

43 

5 

.  1 

w  h  p 

46 

4.0 

C 

20 

43 

5 

7 

wrg 

61.5 

8 

12.2 

C 

21 

47 

4 

8 

gbr 

39 

5 

5-o 

F 

22 

45 

4 

8 

gbr 

39 

5 

10 

". 5 

F 

19 

44 

6 

0 

yg 

7o 

5 

3-5 

F 

20 

47 

4 

8 

wbrP 

39 

5 

12 

1 . 2 

F 

18 

40 

5 

7 

w  br  g 

61 

5 

4.2 

F 

20 

39 

4 

8 

gbr 

39 

5 

13 

5-o 

C 

19 

32 

5 

0 

w  br  g 

43 

8 

14 

4.0 

F 

20 

33 

5 

0 

gbr 

43 

8 

15 

i-5 

Sn 

00 

26 

4 

7 

w  br  g 

37 

2 

16 

3-2 

F 

00 

40 

5 

5 

w  br  g 

56. 

2 

17 

3-7 

F 

22 

33 

5 

6 

w  br  g 

58. 

7 

19 

10.7 

C 

22 

35 

5 

3 

w  br  g 

50. 

5 

20 

3-7 

C 

21 

36 

5 

2 

w  br  p 

48. 

2 

22 

3-4 

F 

22 

38 

6 

5 

yg 

86. 

5 

23 

10.8 

F 

22 

24 

6 

2 

yg 

76. 

5 

24 

3-5 

F 

21 

33 

4 

8 

gbr 

39- 

5 

26 

10.8 

C 

22 

36 

4- 

9 

wbr  p 

41. 

7 

ATMOSPHERIC    NUCLEI. 
Table  49. — Mean  daily  nucleations,  corresponding  to  table  48. 


139 


Date. 

nx  10-3 

Date. 

n  X  io_s 

Date. 

n  X  io~s 

1905. 

1905. 

1905. 

May  4 

11 

June  28 

30 

Aug.  25 

11 

5 

38 

29 

28 

26 

9 

6 

66 

30 

35 

27 

6 

7 

33 

July  1 

3i 

28 

35 

8 

96 

2 

19 

29 

14 

9 

38 

3 

15 

30 

25 

10 

44 

4 

24 

3i 

8 

11 

46 

5 

11 

Sept.  1 

24 

12 

32 

6 

14 

2 

10 

13 

21 

7 

68 

4 

4 

14 

14 

8 

30 

7 

17 

15 

22 

9 

20 

8 

19 

16 

13 

11 

3i 

9 

3i 

17 

18 

12 

36 

11 

22 

18 

26 

13 

30 

12 

15 

19 

34 

14 

34 

13 

16 

20 

46 

15 

16 

14 

29 

21 

25 

16 

19 

15 

3i 

22 

36 

17 

19 

16 

17 

23 

42 

18 

37 

18 

18 

24 

49 

19 

24 

19 

11 

25 

58 

20 

19 

20 

17 

26 

34 

21 

19 

21 

20 

27 

18 

22 

33 

22 

35 

28 

33 

23 

3 

23 

26 

29 

21 

24 

22 

25 

25 

30 

14 

25 

25 

26 

46 

3i 

11 

27 

30 

27 

52 

June  1 

*5 

29 

10 

28 

25 

2 

37 

30 

4 

29 

40 

3 

28 

3i 

7 

30 

28 

4 

29 

Aug.  1 

11 

Oct.  2 

26 

5 

18 

2 

25 

3 

16 

6 

8 

3 

65 

4 

35 

7 

35 

4 

30 

5 

42 

8 

24 

5 

16 

6 

36 

9 

38 

6 

20 

7 

44 

10 

35 

7 

28 

9 

46 

11 

17 

8 

24 

10 

24 

12 

29 

9 

22 

11 

35 

13 

30 

10 

35 

12 

36 

H 

30 

11 

26 

13 

38 

15 

40 

12 

24 

14 

42 

16 

3i 

13 

7 

16 

44 

17 

26 

H 

15 

17 

53 

18 

27 

15 

9 

18 

34 

19 

7 

16 

8 

19 

30 

20 

12 

17 

72 

20 

17 

21 

18 

30 

23 

37 

22 

24 

19 

7 

24 

37 

23 

9 

20 

22 

25 

35 

24 

33 

21 

22 

26 

28 

25 

17 

22 

28 

27 

47 

26 

20 

23 

19 

30 

36 

27 

30 

24 

36 

3i 

36 

140 


VAPOR    NUCLEI    AND    IONS. 


Tabus  49. — Continued. 


Date. 

n  X  io~8 

Date. 

n  X  io-s 

Date. 

n  X  io"8 

1905. 

1905. 

1906. 

Nov.  1 

38 

Dec.  21 

30 

Feb.  9 

38 

2 

39 

1906. 

10 

39 

3 

32 

Jan.  1 

32 

11 

65 

4 

30 

2 

60 

12 

40 

6 

28 

3 

38 

13 

35 

7 

39 

4 

60 

H 

23 

8 

37 

5 

60 

15 

70 

9 

39 

6 

68 

16 

70 

10 

47 

8 

37 

17 

38 

11 

70 

9 

89 

19 

5i 

13 

50 

10 

83 

20 

54 

H 

90 

11 

76 

21 

37 

16 

42 

12 

63 

22 

64 

17 

32 

13 

26 

23 

37 

18 

37 

15 

42 

26 

42 

20 

39 

16 

48 

27 

59 

21 

78 

17 

54 

28 

75 

22 

73 

18 

44 

Mar.  1 

72 

23 

39 

19 

50 

2 

7i 

24 

38 

20 

4i 

3 

32 

27 

37 

22 

35 

5 

39 

28 

38 

23 

45 

6 

56 

Dec.  4 

27 

24 

86 

7 

54 

5 

58 

25 

4i 

8 

39 

6 

47 

26 

36 

10 

55 

7 

39 

27 

61 

12 

50 

8 

48 

29 

68 

13 

44 

9 

20 

30 

60 

H 

44 

11 

59 

3i 

35 

15 

37 

12 

40 

Feb.  1 

58 

16 

56 

13 

67 

2 

7i 

17 

59 

14 

64 

3 

75 

19 

50 

15 

86 

4 

42 

20 

48 

16 

44 

5 

37 

22 

86 

18 

92 

6 

76 

23 

76 

19 

37 

7 

75 

24 

39 

20 

44 

8 

53 

26 

42 

Table  50. — Mean  monthly  nucleations  corresponding  to  table  48. 


Date. 

n  X  io~3. 

Date. 

n  X  io-8. 

1905. 
November . .  . 
December  . .  . 

January 

February .... 

March 

April 

May 

June 

July 

53 
69 
66 
7i 
47 
40 

35 
26 

27 

1905- 

August 

September .  . . 

October 

November .  .  . 
December  .  .  . 

1906. 

January 

February .... 
March 

23 
24 
35 
45 
50 

53 
53 
52 

ATMOSPHERIC    NUCLEI. 


141 


90.  Mean  monthly  nucleations. — The  data  of  table  48  suffice  for  the 
determination  of  the  average  nucleations  per  month,  care  being  taken  to 
omit  the  days  on  which  no  observations  were  taken.  Table  50  contains 
the  results. 

These  data  are  shown 
in  the  lower  graphs  of 
fig.  62.  What  is  re- 
markable is  the  gradual 
rise  of  the  curve  to  a 
persistent  maximum 
reaching  nearly  into 
April.  True,  the  win- 
ter was  relatively  mild 
and  the  spring  relatively 
cold;  but  one  would 
not  be  prepared  to  pre- 
dict nucleations  so  uni- 
formly maintained  be- 
tween November  and 
April.  The  distribution 
is  in  fact  peculiar,  as 
may  be  seen  by  compar- 
ing it  with  the  nuclea- 
tion  of  the  preceding 
years  since  1902,  in  fig. 
63.     The  uniformity  of 


:.b 

FIG. 

62 

nx7(T3 

t 

1.6 

K 

^ — ' 

\ 

X 

1    s 

IS 

,'' 

> 

60 

vn 

s 

' 1 

f 

"^^ 

^ 

^^^i 

r""^- 

H  "  :  • 

<0 

20' 

0 

xW3 

_ ; 

) 

f» 

Positive 
ions 


Negative 
ions 


Nuclei 


Aug.    Sept.     Oct. 


No, 


Dec. 


Feb.      Mar. 


Fig.  62. — Average  monthly  ionization  (thousands  per 
cubic  centimeter),  positive  and  negative  as  stated, 
and  nucleations  (thousands  per  cubic  centimeter), 
observed  between  August,  1905,  and  March,  1906. 


the  new  curve,  the  absence  of  maxima  in  December,  are  striking.  One 
may  note  the  upward  march  of  the  successive  curves  1902-03,  1903-04, 
1904-05. 

9 1 .  Measurement  of  ionization. — To  determine  the  number  of  ions  in 
the  atmosphere,  Ebert's*  well-known  apparatus  was  used.  This  consists 
of  a  tubular  condenser,  the  inner  coat  of  which  is  charged  and  in  con- 
tact with  a  graduated  electroscope.  The  air  to  be  examined  is  passed 
through  the  condenser  by  an  aspirator-fan  propelled  by  clockwork. 
The  air  delivery  of  the  machine  is  also  carefully  standardized. 

In  order  to  test  the  same  air  which  yielded  the  nuclei  for  the  preceding 
measurement,  the  electrical  apparatus  (E,  fig.  576)  was  swung  from  the 
outside  of  a  window  on  a  long  swivel  bracket  (B) .  In  this  way  it  could  be 
drawn  near  the  window  for  charging  and  examination  with  appropriate 


*  H.  Ebert:    Illus.  Aeronaut.     Mittheilungen,  October,  1902,  pp.  1-10. 


142 


VAPOR    NUCLEI    AND    IONS. 


lenses  or  moved  to  a  reasonable  distance  away  from  the  window  during 
the  passage  of  the  air  to  be  tested.    In  winter  all  measurements  must  be 

made  with  a  galvano- 
scope  on  the  outside  of 
the  house.  Thermome- 
ters are  shown  at  T. 

The  difficulties  encoun- 
tered in  using  this  ap- 
paratus in  cold  weather 
will  be  investigated  later 
(section  94).  Here  some 
reference  to  its  constants 
is  in  place.  The  quantity 
of  air  passed  through  the 
condenser  in  the  fiducial 
time  (about  10  minutes) 
was  1.0357  X  io8  cubic 
centimeters;  the  capacity 
of    the    condenser    17.74 

Oct.  Nov.  Dec.  Jan.   Feb.  Mar.   Apr.  May  June  Ju/y   Aug.  Sept.  cm.      Hence     if     V    is     the 

Fig.  63. -Atmospheric  nucleation  (thousands  per  cubic   droP  of  potential  in  volts 
centimeter)  from  October,  1902,  to  March,  1906.  during  the    fiducial  time 

specified, 

0-7.7    v/3°°.~     v-    . 

io357Xio        17.52X10 

denotes  the  charge  in  1  cubic  centimeter  of  air.     As  3.4  X  io~10  is  the 
electrostatic  charge  per  electron, 


70 
60 

FIG. 

63 

t^iti' 

ATM, 
"Di 

NUCL 
/St" 

El 

50 

06 

i9°s 

30 

20 
10 

/ 1 

\ 

P<. 

1 

$| 

S> 

t 

r3 

% 

^ 

L 

-»-r 

nXio_3  = 


Q 


3-4XIO-' 


— ,  nearly, 


shows  the  number  of  ions  per  cubic  centimeter.  Measurements  to  find 
their  velocity  were  not  made,  as  this  would  have  carried  me  too  far  from 
the  purposes  of  this  paper. 

I  may  add  that  a  similar  apparatus  was  installed,  in  which  the  winter 
indraft  of  cold  air  (through  a  condenser),  measured  by  an  anemometer, 
was  utilized.  The  object  here  was  to  determine  the  hourly  variations 
of  ionization.  Though  many  observations  were  taken,  their  meaning  is 
vitiated  by  the  temperature  discrepancy  mentioned  in  section  94.  For 
this  reason,  perhaps,  a  periodicity  similar  to  the  one  discovered  by  Wood 
and  Campbell  (Nature,  April,  1906,  p.  583)  with  stagnant  air  was  not 
detected. 


ATMOSPHERIC    IONS. 


143 


92.  Data  for  ionization. — In  table  51  the  date  and  hour  are  given  in 
the  first  and  second  columns.  The  fall  of  potential,  V-v  (v  being  the 
fall  in  the  absence  of  the  aspirator  air  current),  in  volts,  during  the 
ten  minutes  of  observation,  is  shown  in  the  fourth  column,  marked 
"volts."  From  this  the  charge  (Q)  in  electrostatic  units  per  cubic 
meter,  and  the  number  of  ions  (w)  in  thousands  per  cubic  centimeter, 
are  computed.  The  sign  of  the  charges  is  indicated  in  each  case,  and  q 
denotes  their  ratio  (Q+/Q-).    The  correction  (v)  is  regarded  as  negligible. 


Table  5 


Date. 

Time. 

Volts. 

Q. 

nXio-3. 

Date. 

Time. 

Volts. 

Q. 

nxio~s. 

1905. 

1905. 

July    26 

4.0 

3-7 

+0.21 

0.62 

Aug.     9 

9.2 

10.9 

+  0.62 

1.82 

4.6 

+ 

.26 

.76 

1.7 

-    .  10 

.29 

5-1 

+ 

.29 

.85 

8.2 

+    -47 

1.38 

7-8 

+ 

•  45 

1.32 

5-2 

-    30 

.88 

6.1 

+ 

•  35 

1.03 

6-3 

+  .36 

1.05 

5 

5-9 

+ 

•  34 

1 .00 

4.2 

-  .24 

.70 

29 

9.2 

50 

+ 

.29 

.85 

6-3 

+  .36 

1.05 

5-9 

- 

•  34 

1. 00 

4.2 

-  .24 

.70 

4.0 

6-3 

+ 

•  36 

1 .02 

12.3 

5-2 

+   .30 

.88 

4.2 

- 

•  24 

.70 

6.3 

-  .36 

1.05 

3i 

10. 0 

7-7 

+ 

.44 

1.29 

10 

9-5 

8.2 

+  .47 

1.38 

3-o 

- 

.18 

•52 

5-2 

-    30 

.88 

3-o 

7.8 

+ 

•  45 

1.32 

12 

7.2 

+  .41 

1.20 

59 

- 

•  34 

1 .00 

7.2 

-  .41 

1 .20 

Aug.     1 

10. 0 

2.6 

+ 

•  15 

•44 

11 

10 

6.3 

+  .36 

105 

2.6 

- 

15 

•44 

5-2 

-    30 

.88 

3-o 

6-3 

+ 

.36 

1 .02 

12.3 

8.2 

+  .47 

1.38 

8.1 

- 

.46 

i-35 

5-2 

-  .30 

.88 

2 

9.2 

6.9 

+ 

•  39 

1. 14 

12 

9.0 

6.3 

+  .36 

105 

56 

- 

•  32 

•94 

6.3 

-   36 

1.05 

4.0 

5-9 

+ 

•  34 

1 .00 

12.0 

5-2 

+  .30 

.88 

3-i 

- 

.18 

•52 

6.3 

-  .36 

105 

3 

10. 0 

8.2 

+ 

.47 

1.38 

14 

9-4 

11. 9 

+    .68 

2.00 

5-5 

- 

.31 

•  91 

II. 0 

-      63 

i-85 

4-3 

6.7 

+ 

.38 

1. 11 

II.3 

13.8 

+    .79 

2.32 

4-4 

- 

.25 

•73 

II. 0 

-    -63 

1.85 

4 

10. 0 

5-3 

+ 

•  30 

.88 

12.3 

II. 0 

+    .63 

1.85 

4-4 

- 

•  25 

•73 

II. 0 

-      63 

1.85 

43 

2.6 

+ 

15 

•44 

15 

10 

10 

+    -57 

1.67 

4.8 

- 

•  27 

•79 

8.2 

-     -47 

1.38 

5 

10. 0 

4.2 

+ 

•  24 

.70 

10. 0 

+    -57 

1.67 

5-3 

- 

•  30 

.88 

8.2 

-     -47 

1.38 

4.0 

4.6 
6-5 

+ 

.26 
•  37 

.76 
1.08 

9.1 

27.8 

+      -52 

1 -52 

7 

9-4 

10. 0 

+ 

•  57 

1.67 

12.3 

91 

+    -52 

152 

6-7 

- 

.38 

1 .  11 

91 

-    .52 

1.52 

12.3 

9.0 

+ 

.51 

1.50 

16 

10 

8.2 

+    -47 

1.38 

9-5 

- 

•  54 

1.58 

5-2 

-      30 

.88 

8 

10. 0 

5-5 

+ 

•  31 

•9i 

1 .0 

10. 0 

+    -57 

1.67 

3-2 

- 

.18 

•52 

7.2 

-     -4i 

1.20 

9 

9.2 

6-3 

+ 

•  36 

i. 05 

17 

10. 0 

8.2 

+    -47 

1.38 

5-5 

•  31 

.91 

5-2 

-      30 

.88 

144 


VAPOR    NUCLEI    AND    IONS. 
Tabus  51.— Continued. 


Date. 

Time. 

Volts. 

Q. 

n  x  io-3. 

Date. 

Time. 

Volts. 

2- 

n  X  10-3. 

1905. 

1905. 

Aug.  17 

12.3 

10. 0 

+  c 

•57 

1.67 

Sept.    2 

9-7 

3-7 

-  0.  21 

0.61 

10. 0 

- 

•57 

1.67 

i-4 

6.0 

+ 

•34 

1. 00 

18 

10. 0 

8.2 

+ 

•47 

1.38 

2.  2 

- 

.  12 

•37 

9.1 

- 

•52 

152 

4 

10.5 

5-i 

+ 

.29 

.85 

12.0 

9-i 

+ 

•52 

1  52 

2.8 

- 

.16 

•47 

9-i 

- 

•52 

152 

i-7 

5-4 

+ 

•31 

.91 

19 

9.0 

10. 0 

+ 

•57 

1.67 

10.4 

- 

•  59 

1.74 

9.1 

- 

•52 

152 

7 

10.3 

4.8 

+ 

.27 

.80 

12.0 

3-3 

5-3 
5-4 

+ 

•30 

•3i 

.88 
•9i 

21 

10. 0 

'8.2 

+ 

•47 

1^38 

4.2 

- 

.24 

.70 

9.1 

- 

•52 

152 

8 

10.  2 

7-i 

+ 

.40 

1. 18 

1.0 

7.2 

+ 

.41 

1 .20 

6-5 

- 

•37 

1.09 

2.  I 

- 

.  12 

•35 

2-5 

8.6 

+ 

•49 

1.44 

22 

10 

6-3 

+ 

.36 

1.05 

9-5 

- 

•  54 

i-59 

6-3 

- 

.36 

1.05 

9 

9-7 

50 

+ 

.28 

.84 

1 .0 

3-1 

+ 

.18 

•52 

6.4 

- 

.36 

1 .06 

4.2 

- 

.24 

.70 

2.2 

8.9 

+ 

•  5i 

1.50 

23 

9-3 

10. 0 

+ 

•57 

1.67 

4.2 

- 

.24 

.70 

8.2 

- 

•47 

1.38 

11 

9-9 

3-7 

+ 

.  21 

.61 

12.0 

7.2 

+ 

.41 

1 .20 

4-i 

- 

.23 

.69 

10. 0 

- 

•  57 

1.67 

2.4 

2-3 

+ 

.13 

.38 

24 

10. 0 

6-3 

+ 

.36 

105 

2.8 

- 

.16 

•47 

6-3 

- 

•36 

1.05 

12 

10. 1 

10.8 

+ 

.61 

1.79 

12.0 

4.2 

+ 

•24 

.70 

1.9 

- 

.  11 

•32 

5-2 

- 

•30 

.88 

2.7 

2.2 

+ 

.  12 

.36 

25 

10. 0 

5-2 

+ 

.30 

.88 

3-3 

- 

•19 

.56 

31 

- 

.18 

•52 

13 

10.3 

4-8 

+ 

•27 

•79 

1 .0 

8.2 

+ 

•47 

1.38 

4.0 

- 

.23 

.68 

6.3 

- 

.36 

1.05 

2-3 

4.2 

+ 

•24 

.70 

26 

9.0 

8.2 

+ 

•47 

1.38 

30 

- 

•  17 

•50 

6.3 

- 

.36 

1.05 

14 

10.4 

9.2 

+ 

•52 

1-53 

12.0 

9.1 

+ 

•  52 

152 

6.7 

- 

.38 

1 .  12 

8.2 

- 

•47 

1.38 

2-5 

8.2 

+ 

•47 

i-38 

28 

10.4 

6.2 

- 

•35 

1.05 

7-6 

- 

•43 

125 

3-4 

+ 

.19 

•56 

15 

10.4 

6.0 

+ 

•34 

1. 00 

2.7 

2.4 

- 

H 

.41 

7-7 

— 

.44 

1.29 

3-2 

+ 

.18 

•54 

2-5 

10. 1 

+ 

•  57 

1.68 

29 

9-9 

3-7 

+ 

.  21 

.63 

3-5 

- 

.20 

•59 

3-7 

- 

.  21 

.63 

16 

10.5 

4.2 

+ 

•24 

.70 

2.6 

5-o 

+ 

.29 

.86 

2.4 

- 

•H 

.41 

4-5 

- 

•  25 

.76 

2.0 

8-3 

+ 

•47 

1 .40 

30 

10.5 

4.8 

+ 

.27 

•79 

24 

- 

•14 

•41 

30 

- 

•17 

.48 

18 

10. 0 

2.8 

+ 

.16 

•47 

2.6 

4-5 

+ 

.25 

.76 

5-3 

- 

•30 

.88 

5-i 

- 

.29 

.85 

3-5 

8-3 

+ 

•47 

1.40 

3i 

10. 0 

3-o 

+ 

•  17 

•  50 

2.8 

- 

.16 

•47 

5-6 

- 

32 

•94 

19 

9.8 

7-7 

+ 

•44 

1.29 

2.7 

5-9 

+ 

•34 

1. 00 

1.8 

- 

.  10 

•3i 

4.2 

- 

•24 

•7i 

3-3 

3-3 

+ 

•  19 

.56 

Sept.    1 

10.5 

5-4 

+ 

•3i 

•9i 

2-3 

- 

.13 

.38 

4-7 

- 

.27 

•  79 

20 

10.2 

3-5 

+ 

.20 

•59 

3 

6.8 

+ 

•39 

1. 14 

1 . 2 

- 

.07 

.20 

•4 

- 

•23 

.67 

3-7 

4-7 

+ 

.27 

•79 

2 

9-7 

5-i 

+ 

.29 

.85 

4.2 

•24 

.70 

ATMOSPHERIC    IONS. 

M5 

Table  51.- 

-Continued. 

Date. 

Time. 

Volts. 

Q. 

n  X  10-8. 

Date. 

Time. 

Volts. 

Q. 

n  X  io-s. 

1905- 

1905. 

Sept.  21 

8.7 

8.3 

+  0 

•47 

1.40 

Oct.      7 

2.6 

3-5 

-0 

.20 

o.59 

4.2 

- 

.24 

.70 

9 

12  1 

8.7 

+ 

50 

1 .46 

3-5 

4-5 

+ 

.26 

.76 

7.2 

- 

•  41 

1.20 

4.6 

- 

.26 

•76 

4-5 

16.6 

+ 

•  95 

2-79 

22 

9.8 

1.9 

+ 

.  11 

•32 

2-4 

- 

•  14 

•4i 

2.6 

- 

•  15 

•44 

10 

9-9 

2.8 

+ 

.16 

•47 

50 

2.8 

+ 

.16 

•47 

4.8 

- 

.27 

•79 

2.4 

- 

•14 

.41 

2-5 

4.2 

+ 

24 

.70 

23 

9.0 

7-8 

+ 

44 

1.30 

8.1 

- 

.46 

1-35 

7-7 

- 

•44 

1.29 

1 1 

9-8 

6.0 

+ 

.34 

1 .00 

25 

11. 0 

8-3 

+ 

47 

1.40 

8.9 

- 

51 

150 

95 

- 

•54 

i-59 

2.  2 

2-3 

+ 

13 

•38 

2.7 

5-3 

+ 

30 

.88 

4.2 

- 

•  24 

.70 

10. 1 

- 

.58 

1. 71 

12 

9.0 

3-4 

+ 

.19 

•57 

26 

9.0 

4-5 

+ 

.26 

.76 

8.9 

- 

.51 

150 

4.1 

- 

23 

.69 

2.7 

6-3 

+ 

•  36 

1 .02 

3-7 

6.8 

+ 

•39 

1. 14 

7-7 

- 

•  44 

1.29 

9-3 

- 

•53 

1.56 

13 

11. 0 

3-7 

+ 

.21 

.61 

27 

9.0 

4-5 

+ 

.26 

.76 

8-9 

- 

•  51 

1.50 

2.7 

- 

•  15 

.46 

2.6 

1.4 

+ 

.08 

•23 

5-5 

1 . 1 

+ 

.06 

•19 

3-o 

- 

•  17 

•48 

3-5 

- 

.20 

•  59 

14 

10. 0 

7.2 

+ 

.41 

1 .20 

28 

9-5 

3-7 

4- 

.21 

.61 

7-i 

- 

.40 

1. 18 

4.8 

- 

.27 

•  79 

2.6 

4-9 

+ 

.28 

.82 

3-4 

8.3 

+ 

•47 

1.40 

4.2 

— 

•  24 

•70 

5-4 

- 

•3i 

•9i 

16 

2-5 

5-9 

+ 

•  34 

1. 00 

29 

9.2 

7.0 

+ 

.40 

1.17 

3-7 

- 

.21 

.61 

6.8 

- 

•39 

1. 14 

4-7 

M 

+ 

.08 

•23 

2-5 

2.4 

+ 

•14 

.41 

2.4 

- 

.14 

.41 

1.8 

- 

.  10 

•31 

17 

10.3 

6.1 

+ 

35 

1.03 

30 

9.0 

1.9 

+ 

.  11 

•32 

7-4 

- 

•  42 

1.23 

30 

- 

.17 

.48 

2.7 

7-5 

+ 

•  43 

1.26 

3-2 

3-7 

+ 

.21 

.61 

3-5 

- 

.20 

•59 

1.4 

- 

.08 

.23 

18 

9.2 

30 

+ 

•  17 

.48 

Oct.      2 

9-i 

2-3 

+ 

•13 

.38 

8.0 

- 

.46 

1-35 

24 

- 

.14 

.41 

2.7 

2.4 

+ 

•  14 

•4i 

2.7 

1.8 

+ 

.10 

•31 

2-4 

l- 

.14 

.41 

2.4 

- 

.14 

•4i 

19 

12 

4.2 

+ 

•  24 

.70 

3 

10. 0 

3-6 

+ 

.20 

.60 

7-4 

- 

42 

1.23 

30 

- 

17 

•50 

3-5 

6.7 

+ 

•  38 

1 .  12 

2.8 

7-9 

+ 

•45 

131 

4.8 

- 

27 

•79 

4-8 

- 

.27 

•  79 

20 

11. 6 

6.4 

+ 

•  36 

1.07 

4 

9.8 

36 

+ 

.20 

.60 

2.8 

- 

.16 

•47 

4.2 

- 

.24 

.70 

2.6 

6-5 

+ 

.37 

1.09 

2-9 

3-o 

+ 

•17 

•48 

1.9 

- 

.  11 

•32 

3-6 

- 

.20 

.60 

23 

12.2 

4-2 

+ 

•  24 

.70 

5 

10.5 

24 

+ 

.14 

•41 

6.9 

- 

•  39 

1. 14 

6.0 

- 

•34 

1. 00 

4-3 

6.4 

+ 

.36 

1.07 

6 

9.2 

6.6 

+ 

•38 

1. 11 

7-7 

- 

•  44 

1 .29 

9-5 

- 

•54 

i-59 

24 

10.2 

i-7 

+ 

.10 

29 

31 

7.2 

+ 

.41 

1 .20 

3-3 

- 

.19 

56 

10.4 

- 

•59 

i-74 

2.7 

3-1 

+ 

.18 

•52 

7 

9.2 

6.5 

+ 

•37 

1 .09 

1.8 

- 

.  10 

•3i 

6.6 

- 

•38 

1. 11 

25 

12. 1 

6.2 

+ 

•  35 

1.05 

2.6 

3-6 

+ 

.  20 

.60 

8.2 

* 

•  47 

1-38 

146 


VAPOR    NUCLEI    AND    IONS. 
Table  5 1 .  —Continued. 


Date. 

Time. 

Volts. 

Q- 

WXIO-3. 

Date. 

Time. 

Volts. 

Q. 

n  X  io~3. 

1905. 

1905- 

Oct.    25 

4.0 

i-4 

+  0.08 

0.23 

Nov.   14 

10.7 

5-4 

-c 

►•31 

•9i 

3-6 

- 

.  20 

.60 

16 

2-5 

3 

3 

+ 

•19 

•56 

26 

2.7 

5-6 

+ 

•32 

•94 

6 

8 

- 

•39 

1. 14 

H-3 

- 

•65 

1. 91 

17 

1 1 . 2 

3 

6 

+ 

.  20 

.60 

4.6 

6.9 

+ 

•39 

1. 14 

4 

2 

- 

•24 

.70 

9.6 

- 

•55 

1 .62 

2.7 

2 

8 

+ 

.16 

•47 

27 

11. 0 

5-6 

+ 

•32 

•94 

8 

4 

- 

.48 

1. 41 

8-3 

- 

•47 

1 .40 

18 

9-8 

4 

6 

+ 

.26 

•76 

2.8 

6.0 

+ 

•34 

1 .00 

10 

4 

- 

•59 

1.74 

4.2 

- 

.24 

•7i 

20 

2.7 

1 

7 

+ 

.  10 

•29 

30 

2.5 

3-4 

+ 

19 

•57 

8 

1 

- 

.46 

1-35 

10.5 

- 

.60 

1 .76 

21 

10.6 

2 

4 

+ 

.14 

•41 

4-7 

6-3 

+ 

•36 

1 .02 

7 

1 

- 

.40 

1. 18 

30 

- 

17 

.48 

3-2 

5 

3 

+ 

•30 

.88 

3i 

11. 4 

2.4 

+ 

.14 

.41 

5 

4 

- 

•3i 

•9i 

8.9 

- 

51 

1.50 

22 

12. 1 

7 

7 

+ 

•44 

1 .  29 

3-7 

30 

+ 

•17 

.48 

6 

6 

- 

.38 

1 .  11 

7-7 

- 

•44 

1.29 

4.0 

1 

8 

+ 

.  10 

•3i 

Nov.     1 

30 

8-7 

+ 

•50 

1 .46 

6 

8 

- 

•39 

1. 14 

2.8 

- 

.16 

•47 

23 

2.7 

5 

9 

+ 

•34 

1 .00 

5-6 

6-7 

+ 

.38 

1. 12 

1 

8 

- 

.  10 

•31 

6.0 

- 

•34 

1. 00 

24 

2-5 

3 

7 

+ 

.  21 

.61 

2 

2-4 

6.7 

+ 

.38 

1 .  12 

3 

0 

- 

17 

.48 

9-5 

- 

54 

1. 59 

5-3 

1 

8 

+ 

.  10 

•31 

3 

2.7 

1.8 

+ 

.  10 

•31 

2 

3 

- 

•13 

.38 

30 

- 

•  11 

•  50 

27 

3-4 

5 

3 

+ 

•30 

.88 

50 

6.0 

+ 

•34 

1. 00 

6 

6 

- 

•38 

1 .  11 

2.4 

- 

•14 

•41 

5-3 

7 

8 

+ 

•45 

132 

4 

10.2 

t-4 

+ 

.08 

•23 

2 

3 

- 

•13 

•38 

2.4 

— 

.14 

.41 

28 

10.5 

1 

8 

+ 

.  10 

•3i 

2.4 

2.8 

+ 

.16 

•  47 

4 

5 

- 

.26 

•76 

2.2 

- 

.  12 

36 

3-o 

4 

8 

+ 

•27 

•79 

6 

30 

7.2 

+ 

.41 

1 .  20 

5 

7 

- 

•32 

.96 

3.0 

- 

•17 

•50 

Dec.     4 

12.0 

5 

4 

+ 

•31 

•91 

7 

10.6 

6.2 

+ 

•35 

105 

4 

2 

- 

.24 

.70 

9-5 

- 

•54 

i-59 

2-7 

2 

4 

+ 

.14 

•41 

2.8 

5-8 

+ 

•33 

•97 

11 

9 

- 

.68 

2.0 

4-4 

- 

•25 

•73 

5 

11. 0 

12 

7 

+ 

•73 

2.15 

8 

30 

5-3 

+ 

•30 

.88 

11 

9 

- 

.68 

2.00 

30 

- 

•17 

•50 

2-7 

12 

0 

+ 

.68 

2.01 

9 

2-5 

2.3 

+ 

•13 

.38 

6 

9 

- 

•39 

1. 14 

11 . 1 

- 

63 

1.85 

6 

12.2 

9 

5 

+ 

54 

i-59 

10 

11 . 1 

4-7 

+ 

•27 

•79 

3 

0 

- 

•17 

•  50 

8-3 

- 

•47 

1.40 

2.7 

2 

8 

+ 

.16 

•47 

30 

1.8 

+ 

.  10 

•3i 

3 

6 

— 

.  20 

.60 

3-6 

- 

.20 

.60 

7 

2.7 

10 

5 

+ 

.60 

1.76 

11 

10.5 

3-9 

+ 

.  22 

65 

4 

5 

- 

.26 

.76 

5-4 

- 

•3i 

•  9i 

8 

11 . 2 

9 

5 

+ 

•54 

i-59 

2-5 

4.8 

+ 

.27 

•79 

2 

4 

- 

•14 

•41 

8.1 

- 

.46 

i-35 

3-2 

7 

3 

♦ 

•42 

1.24 

13 

12.4 

6.8 

+ 

•39 

1. 14 

2 

3 

- 

•13 

.38 

6.0 

- 

•34 

1 .00 

9 

10.7 

6 

7 

+ 

•38 

1. 12 

3-2 

•9 

+ 

05 

.16 

5 

9 

- 

•34 

1 .00 

5-6 

- 

•32 

•<H 

1 1 

30 

7 

6 

+ 

•43 

1   25 

14 

10.7 

9.8 

+ 

56 

165 

4 

9 

.28 

.82 

ATMOSPHERIC    IONS. 
Table  51. —Continued. 


M7 


Date. 

Time. 

Volts. 

Q- 

nx  10-3. 

Date. 

Time. 

Volts. 

Q. 

nX  io~3. 

1905. 

1906. 

Dec.    1 2 

10.7 

11 .0 

+0.63 

1.85 

Jan.      9 

11 .0 

9-3 

+0.53 

1.56 

i-4 

-   .08 

•23 

3-8 

— 

.  22 

.65 

2.7 

4-7 

+   .27 

79 

3-o 

10.5 

+ 

.60 

1.76 

5-9 

-    -34 

1. OO 

5-1 

— 

.29 

•85 

13 

12.2 

"•3 

+    .65 

1. 91 

10 

3-5 

10.6 

+ 

.60 

1.78 

9-5 

-    -54 

1-59 

14 

— 

.08 

•23 

3-5 

7-7 

+    .44 

1.29 

11 

12.5 

9-7 

4- 

•55 

1.62 

4-4 

-    -25 

•73 

4.2 

— 

.24 

.70 

H 

3-7 

1.9 

+    .11 

•32 

4-7 

13-4 

+ 

.76 

2.02 

4-7 

-    .27 

•79 

2-4 

— 

.14 

.41 

15 

11 .0 

12.7 

+    -73 

2-15 

12 

11 .  2 

4.1 

+ 

•23 

.69 

4-7 

-    .27 

•79 

3-2 

— 

.18 

•54 

16 

3-5 

H-3 

+    .82 

2.41 

4.8 

6-5 

+ 

•37 

1.09 

3-4 

-    .19 

•57 

3-4 

— 

.19 

•57 

18 

4.0 

8.4 

+    .48 

1.41 

13 

10.5 

16.0 

+ 

•9i 

2.68 

2.9 

-    .16 

•49 

6.7 

— 

•38 

1 .  12 

19 

10.5 

6.7 

+    .38 

1 .  12 

3-2 

?21.5 

+  1 

•23 

3.62 

4.1 

-    -23 

.69 

2-3 

— 

•13 

.38- 

2.4 

7.6 

+    -43 

1.25 

15 

10. 0 

6.7 

+ 

•38 

1. 12 

14.8 

-    -84 

2.47 

5-9 

— 

•34 

1 .00 

20 

10.5 

6.8 

+    -39 

1. 14 

16 

11. S 

6.6 

+ 

•38 

1. 11 

4-9 

-    .28 

.82 

1.9 

- 

•32 

3-9 

6.0 

+    -34 

1. 00 

3-4 

5-7 

+ 

•32 

.96 

4-7 

-    .27 

•79 

3-7 

— 

.  21 

•63 

21 

10.5 

"•3 

+    .65 

1. 91 

17 

10. 0 

7.0 

+ 

.40 

1. 17 

6.5 

-    -37 

1.09 

i-9 

— 

.  11 

•32 

30 

3-7 

+    .21 

.61 

3-5 

7.0 

+ 

.40 

1. 17 

3-o 

-    .17 

•48 

5-3 

— 

•30 

.88 

1906, 

18 

12.  2 

7-i 

+ 

.40 

1. 18 

Jan.      1 

3-7 

"•3 

+    .65 

1. 91 

i-7 

— 

.  10 

.29 

4.6 

-    .26 

.76 

4.8 

3-4 

+ 

•19 

•57 

2 

10.7 

190 

+  2.09 

6.01 

1 . 1 

— 

.06 

.18 

10.  2 

-    .58 

1.70 

19 

9-9 

6.6 

+ 

•38 

1 .  11 

3-5 

18.0 

+  1.03 

3.01 

4.2 

— 

•24 

.70 

4-4 

-    -25 

•73 

2-7 

9-7 

+ 

•55 

1.62 

3 

11. 7 

9-5 

+    -54 

i-59 

7-7 

— 

•44 

1.29 

7.0 

-    .40 

1. 17 

20 

10.3 

7-i 

+ 

.40 

1. 18 

3-3 

9-7 

+    -55 

1.62 

31 

— 

.18 

•52 

i-4 

-    .08 

•23 

3-2 

2.8 

+ 

.16 

•47 

4 

12.8 

8.1 

+    .46 

i-35 

3-7 

— 

.  21 

.61 

2.4 

-      H 

.41 

22 

12.5 

7.8 

+ 

•45 

1.32 

3-2 

2-3 

+      13 

•38 

5-4 

— 

•3i 

•9i 

4.2 

-    .24 

.70 

4.0 

4-7 

+ 

•27 

•79 

5 

10. 0 

n. 9 

+    .68 

2.00 

6-3 

— 

•36 

1 .02 

7-5 

-    -43 

1.26 

23 

10.3 

5-3 

+ 

•30 

.88 

2.7 

10. 1 

+    -57 

1.68 

3-4 

— 

.19 

•57 

13- 7 

-    .78 

2.  29 

5-o 

8.1 

+ 

.46 

1-35 

6 

10.6 

9.2 

+    .52 

"53 

2-3 

— 

•13 

•38 

5-4 

-    -3i 

.91 

24 

10. 0 

8.4 

+ 

•48 

1. 41 

4-3 

"•3 

+    .65 

1. 91 

9.6 

- 

•55 

1.62 

5-8 

-    -33 

•97 

25 

9-8 

11 . 2 

+ 

.64 

1.88 

8 

12.5 

12.5 

+    -7i 

2.01 

4-3 

— 

•24 

•73 

6.5 

-    -37 

1.09 

3-1 

7.2 

+ 

.41 

1 .  20 

4-5 

13.0 

+    -74 

2.02 

4-2 

— 

.24 

.70 

7.2 

-    -4i 

1.20 

26 

10. 0 

8-9 

4- 

•5i 

1.50 

148 


VAPOR    NUCLEI    AND    IONS. 
Table  51.— Continued. 


Date. 

Time. 

Volts. 

* 

3 
n  X  io~3. 

Date. 

Time. 

Volts. 

Q- 

n  X  io~8. 

1906. 

1906. 

Jan.  26 

10. 0 

1.9 

—  0. 11 

0.32 

Feb.  8 

9-8 

4-8 

+0.27 

0.79 

3-3 

11 

•3 

+ 

•65 

1. 91 

12.6 

5 

2 

+ 

•30 

.88 

3 

.0 

— 

•  J7 

.48 

11 

.  2 

— 

.64 

1.88 

27 

10.  2 

7 

•5 

+ 

•43 

1.26 

3-4 

8 

.6 

+ 

•49 

i-45 

4 

•9 

— 

.28 

.82 

3 

•3 

— 

.19 

•56 

4.4 

8 

0 

+ 

.46 

i-35 

4.8 

3 

8 

+ 

.22 

.64 

1 

8 

— 

.  10 

•3i 

3 

9 

— 

.22 

.66 

29 

12 

16 

1 

+ 

.92 

2.70 

9 

11. 5 

7 

7 

+ 

•44 

1.30 

5 

0 

— 

.28 

.84 

6 

2 

— 

•35 

1 .04 

3-7 

10 

0 

+ 

•57 

1.67 

1 

9 

+ 

.  11 

•33 

6 

2 

— 

•35 

1.05 

4.9 

5 

9 

+ 

•34 

1. 00 

30 

10.5 

5 

3 

+ 

•30 

.88 

1 

4 

— 

.08 

•23 

7 

2 

— 

.41 

1 .  20 

10 

9-9 

5 

4 

+ 

•31 

•9i 

3-o 

4 

8 

+ 

•27 

•79 

3 

3 

+ 

.19 

.56 

4 

2 

— 

.24 

.70 

10.6 

2 

8 

— 

.16 

•47 

3i 

12.3 

8 

3 

+ 

•47 

1 .40 

10.6 

4 

2 

+ 

.24 

•7i 

7 

5 

— 

•43 

1.26 

12.5 

8 

1 

+■ 

.46 

i-37 

3-2 

8 

9 

+ 

•5i 

1.50 

4 

6 

— 

.26 

•  76 

6 

5 

— 

•37 

1 .09 

5-o 

3 

7 

+ 

.  21 

.62 

Feb.  1 

12.0 

11 

1 

+ 

.63 

1.87 

3 

3 

— 

.19 

.56 

6 

9 

— 

•39 

1. 14 

11 

10.  2 

12 

3 

+ 

.70 

2.06 

5-o 

6 

8 

+ 

•39 

1. 14 

6 

0 

— 

•34 

1 .00 

1 

8 

— 

.  10 

•3i 

6 

5 

+ 

•37 

1 .  10 

2 

11 .0 

12 

3 

+ 

.70 

2.07 

11 

6 

4 

— 

•37 

1.08 

7 

0 

— 

.40 

1. 17 

6 

7 

+ 

•38 

1 .  12 

5-o 

11 

9 

+ 

.68 

2.00 

4-5 

7 

0 

+ 

.40 

1. 18 

2 

4 

— 

.14 

.41 

4 

3 

— 

.24 

•73 

3 

10.  2 

9 

5 

+ 

•54 

1-59 

6 

1 

+ 

•34 

1.03 

4 

7 

— 

.27 

•79 

12 

9-7 

8 

7 

4- 

•50 

1.47 

6.0 

1 

8 

+ 

•  l7 

•52 

7 

8 

— 

•45 

1.30 

3 

5 

— 

.20 

•59 

12 

7 

7 

4- 

•44 

1.30 

4 

10. 0 

8 

6 

+ 

•49 

1.44 

8 

7 

— 

•5o 

1.47 

6 

8 

— 

•39 

115 

3 

7 

8 

+ 

•45 

1.32 

12.4 

3 

7 

+ 

.  21 

.62 

3 

4 

— 

•19 

•57 

8 

4 

— 

.48 

1.40 

13 

!2-5 

5 

4 

+ 

•3i 

.91 

6.2 

5 

6 

+ 

•32 

•94 

0 

.0 

.0 

6 

0 

— 

•34 

1. 00 

5.7 

4 

7 

+ 

.27 

•79 

5 

5-o 

9 

0 

4- 

•5i 

150 

3 

0 

— 

17 

50 

1 

4 

— 

.08 

•23 

14 

12.5 

5 

4 

+ 

•3i 

.91 

6 

9-5 

7 

7 

+ 

•44 

1.30 

5 

— 

•03 

.09 

2 

9 

— 

•17 

•50 

4.7 

1 

6 

+ 

.09 

.28 

11. 6 

7 

6 

+ 

•43 

1.28 

2 

9 

— 

.16 

.48 

1 

4 

— 

.08 

•23 

15 

12.5 

4 

2 

+ 

•24 

.70 

12. 1 

4 

4 

♦ 

.25 

•73 

2 

8 

— 

.16 

•47 

4 

I 

+ 

.23 

.69 

5-2 

7 

T 

+ 

.40 

1. 18 

30 

2 

2 

— 

•13 

•38 

3 

4 

— 

.19 

•57 

9 

+ 

•05 

•15 

16 

I25 

7 

3 

+ 

.42 

1.24 

7 

9.9 

2 

5 

+ 

.14 

•43 

7 

1 

— 

.40 

1. 18 

5 

3 

— 

•30 

•89 

5-o 

5 

0 

+ 

.29 

.86 

12. 

10 

3 

+ 

•59 

1.74 

3 

7 

— 

.21 

.61 

10 

1 

— 

•58 

1.70 

17 

12.2 

4 

2 

+ 

.24 

.70 

3-6 

9 

0 

+ 

•5i 

i-5i 

2. 

8 

— 

.16 

•47 

4 

1 

— 

•23 

.69 

3-4 

4- 

2 

+ 

•24 

71 

6.2 

2 

8 

+ 

.16 

•47 

1 . 

7 

— 

.  10 

•29 

5 

4 

•3i 

.89 

19 

12.2 

5 

3 

4- 

•30 

.89 

ATMOSPHERIC    IONS. 
Table  51.— Continued. 


149 


Date. 

Time. 

Volts. 

(?• 

n  X  10-3. 

Date. 

Time. 

Volts. 

Q 

n  X  io-'. 

1906. 

1906. 

Feb.  19 

12.2 

4.4 

-O.25 

o.73 

Mar.  6 

5-o 

4.0 

+0 

.  22 

0.66 

5-o 

3 

8 

+ 

.22 

.64 

3-i 

— 

.18 

•52 

3 

4 

— 

.19 

•57 

7 

J2.5 

7-9 

+ 

•45 

1.32 

20 

11. 2 

8 

7 

+ 

50 

1-47 

6.2 

— 

•35 

105 

4 

3 

— 

.24 

•73 

3-7 

4.0 

+ 

.  22 

1. 17 

5-o 

4 

7 

+ 

.27 

•79 

2.8 

— 

.16 

47 

2 

8 

— 

.16 

•47 

8 

12.2 

7-3 

+ 

.42 

2.15 

21 

5-3 

5 

4 

+ 

•31 

.91 

4.2 

— 

•24 

•7i 

4 

2 

— 

.24 

•7i 

5-o 

3-7 

+ 

.  21 

1.09 

22 

12.0 

6 

8 

+ 

•39 

115 

4.2 

— 

.24 

71 

6 

O 

— 

•34 

1 .00 

10 

w.J 

6.2 

+ 

•35 

105 

23 

4-7 

6 

0 

+ 

•34 

1. 00 

4.2 

— 

•24 

•7i 

4 

7 

— 

.27 

•79 

3-5 

5-i 

+ 

.29 

•85 

26 

4-3 

8 

1 

+ 

.46 

i-37 

1.4 

— 

.08 

•23 

5 

8 

— 

•33 

•97 

12 

1.2 

8-7 

+ 

•  50 

1.47 

6 

7 

+ 

•38 

1 .  12 

9.0 

— 

•  51 

150 

27 

H.3 

9 

0 

+ 

•51 

150 

4.2 

5-2 

+ 

.29 

?  .87 

5 

5 

— 

•3i 

.91 

4-7 

— 

•27 

•79 

5-o 

5 

1 

+ 

.29 

.85 

13 

5 

5-9 

+ 

•34 

1 .00 

3 

3 

— 

.19 

.56 

3-6 

— 

.20 

.60 

28 

12.2 

9 

4 

+ 

•54 

1-59 

14 

4 

4-8 

+ 

•27 

79 

6 

6 

— 

•38 

1. 11 

3-i 

— 

•  17 

•5o 

5-o 

8 

5 

+ 

.48 

i-43 

15 

i-5 

7.0 

+ 

.40 

1. 17 

5 

6 

— 

•3i 

.91 

6.2 

— 

•35 

105 

Mar.  1 

12.5 

9 

4 

+ 

•54 

1.59 

16 

3-2 

8-3 

+ 

•47 

1.38 

6 

5 

— 

•37 

1.09 

3-7 

— 

.21 

1 .09 

50 

5 

9 

+ 

•34 

1. 00 

17 

3-7 

2.4 

+ 

.14 

.41 

6 

0 

— 

•34 

1 .00 

2.6 

— 

•  15 

•44 

2 

"•5 

6 

3 

+ 

•36 

1.06 

19 

10.7 

6.2 

+ 

•35 

1.05 

5 

7 

— 

•32 

.96 

3-7 

— 

.21 

1 .09 

5-7 

3 

3 

+ 

.19 

56 

20 

3-7 

3-4 

+ 

.19 

•57 

3 

2 

— 

.18 

•54 

4.4 

— 

.25 

•73 

3 

10.7 

4 

2 

+ 

•24 

•7i 

22 

3-4 

50 

+ 

.28 

.84 

9 

3 

— 

•53 

i-57 

5-2 

— 

•30 

.88 

5 

'2-5 

10 

6 

+ 

.61 

1.79 

23 

10.7 

7-9 

+ 

•45 

1.32 

7 

5 

— 

•43 

1.26 

6.7 

— 

•38 

1 .  12 

4-5 

10 

5 

+ 

.60 

1.76 

24 

3-5 

2.8 

+ 

.16 

•47 

3 

5 

— 

.20 

•59 

2.8 

— 

.16 

•47 

6 

H-5 

6 

6 

+ 

•38 

1 .  11 

26 

10.8 

6.4 

+ 

•36 

1.06 

4 

s 

27 

•79 

5-1 

_ 

.29 

•85 

93.  Remarks  on  the  tables. — Perhaps  the  most  expeditious  way  of 
digesting  this  large  body  of  observations  is  to  plot  them  graphically 
(as  above,  figs.  58-61)  in  relation  to  time.  This  was  carefully  done 
throughout,  and  the  statements  now  to  be  made  refer  to  this  summary. 
It  is  not  probable  that  positive  and  negative  ions  will  show  the  same 
fluctuations  in  number,  but  a  general  similarity  in  the  trend  of  the 
curves  may  be  anticipated. 

Beginning  with  August,  1905,  the  positive  and  negative  ionizations 
usually  vary  in  the  same  sense,  though  rarely  in  the  same  absolute  magni- 


150  VAPOR    NUCLEI    AND    IONS. 

tude.  There  being  but  two  observations,  as  a  rule,  for  the  day,  the  nature 
of  the  fluctuations  is  not  referable  to  periods;  and  indeed  there  is  as 
liable  to  be  a  rise  as  a  fall  of  values  during  the  middle  hours  of  the  day. 
Towards  the  end  of  the  month  and  in  the  beginning  of  September  there 
is  an  absence  of  agreement  in  the  march  of  positive  and  negative  ioni- 
zations. Frequently  the  variation  of  one  ionization  is  apt  to  lag  behind 
the  other. 

After  the  7  th  of  September  the  positive  and  negative  variations 
tend  to  take  the  same  sign  again,  but  the  agreement  in  the  course  of  a 
month  is  less  marked  than  before. 

In  October  the  earlier  observations  are  as  a  rule  in  the  same  phase  until 
October  10,  where  the  first  of  a  series  of  anomalies  occurs,  to  be  specially 
considered  later  (section  94).  While  the  data  throughout  the  remaining 
part  of  October  are  regular,  there  are  similarly  displaced  variations 
towards  the  end,  which  run  quite  into  the  next  month. 

During  November  similarity  of  variation  of  the  positive  and  negative 
ionization  may  still  be  recognized,  but  in  December  the  divergence  of 
data  is  so  marked  that  it  is  not  possible  to  coordinate  them ;  and  the  same 
discrepancy  shows  itself  in  January,  both  as  regards  the  signs  of  vari- 
ations and  their  absolute  values.  One  may  note,  moreover,  that  the 
positive  curve  (the  observations  for  which  were  first  taken)  is  more 
irregular  in  its  march  and  fluctuates  between  relatively  enormous  values. 
Though  there  is  some  agreement  in  phase  between  January  18  and.  25, 
the  anomalies  increase  again  at  the  close  of  the  month. 

The  attempt  was  therefore  made  in  February  (section  94)  to  account 
for  and  remove  these  discrepancies,  and  though  this  was  but  partially 
successful,  the  positive  and  negative  results  during  the  remainder  of  the 
season  again  return  to  an  unmistakable  agreement  in  character.  There 
is,  moreover,  a  curious  parallelism  between  the  general  march  of  the 
nucleation  curves  and  the  ionization  after  February  15  as  far  as  March. 
In  the  latter  month  the  positive  and  negative  ionizations,  though  at  first 
fluctuating  and  uncertain,  are  finally  in  very  close  agreement. 

From  what  has  been  stated  it  appears  that  the  positive  results  during 
December  and  January  are  liable  to  be  untrustworthy.  The  negative 
results,  which  were  taken  after  the  positive,  show  less  irregular  fluctua- 
tion and  are  in  a  measure  acceptable  throughout  the  eight  months  of 
observation. 

94.  Errors  of  measurement. — The  abnormal  data  during  the  occurrence 
of  cold  weather,  and  as  a  rule  in  December  and  January,  show  that  some 
grave  error  must  here  have  crept  into  the  results.  As  every  part  of  the 
condenser  and  appurtenances  functioned  faultlessly,  this  error  is  liable 


ATMOSPHERIC    IONS.  151 

to  be  found  in  the  galvanoscope.  Changes  of  temperature  produce  vorti- 
cal currents  in  the  capsule  which  modify  the  deflections  of  the  aluminum 
foils.  In  the  mean  ranges,  one  scale  part  of  double  deflection  is  equivalent 
to  about  6  volts,  or  to  1,000  ions  per  cubic  centimeter.  Therefore,  the 
presence  of  any  secondary  disturbance  like  the  one  in  question  is  of  very 
serious  consequence.  Prior  to  measurement,  the  apparatus  was  naturally 
left  in  the  cold  air  out  of  doors  until  temperature  uniformity  was  pre- 
sumable; but  this  is  not  sufficient,  as  the  special  observations  in  the 
early  part  of  February  show,  even  for  a  galvanoscope  dried  with  sodium. 

Turning  first  to  the  leakages  due  to  conduction,  etc.  (v  in  the  above 
equation),  direct  experiments  made  at  different  times  showed  values  of 
0.073,  0.067,  0.120  volt  per  minute,  or  less  than  0.9  volt  for  the  ten 
minutes  of  observation.  This  is  equivalent  to  an  excess  of  150  ions  per 
cubic  centimeter.  As  it  is  applied  equally  to  the  positive  and  to  the 
negative  ions,  is  independent  of  the  size  of  the  deflections,  and  the  same 
no  matter  whether  the  deflections  on  both  sides  are  equal  or  not,  it  has 
no  bearing  on  the  outstanding  errors  in  question.  It  was  not  deducted 
from  the  ionizations  (n)  of  table  53,  which  are  therefore  slightly  too  large. 

Trials  made  between  February  4  and  1 1  showed  that  in  almost  every 
case  the  first  measurements  (whether  for  positive  or  negative  ions) ,  even 
after  the  galvanoscope  had  been  exposed  to  the  cold  air  for  some  time,  are 
too  large.  This  discrepancy  may  at  times  extend  to  the  second  and  third 
observations  (February  6,  9,  11).  Thus  on  February  9  the  estimated 
positive  ionization  would  be  a  thousand  and  zero,  for  instance.  Usually, 
however,  the  second  and  third  observations  are  liable  to  be  trustworthy 
(February  6,  10,  11,  etc.).  Hence  electroscopic  apparatus  which  can  not 
be  left  permanently  out  of  doors,  but  is  taken  from  a  warm  room  into 
the  cold  atmosphere,  even  if  it  is  sodium  dried,  is  not  liable  to  show  war- 
rantable results  after  mere  waiting  for  uniform  temperature.  It  seems 
additionally  necessary  to  pass  a  large  volume  of  cold  air  through  the 
condenser,  or  to  make  successive  measurements  in  series.  The  observer 
is  usually  in  doubt,  whenever  the  positive  and  negative  ionizations  differ 
widely,  so  that  at  least  three  tests  must  be  made.  The  tendency  of  the 
apparatus  to  show  spurious  results  is  usually  indicated  by  an  inequality 
of  deflections  of  the  foils  on  either  side  of  the  vertical.  They  may  increase 
to  a  maximum  after  charging  and  then  decrease  regularly.  The  latter 
probably  finds  an  explanation  in  the  gradual  cessation  of  a  down-pouring 
cold  air  current  near  the  sides  of  the  capsule  of  the  galvanoscope,  but  the 
persistence  of  unequal  deflections  must  follow  from  other  causes.  Re- 
membering that  the  air  is  desiccated  internally  with  metallic  sodium,  it 
seems  hardly  creditable  that  there  can  be  a  precipitation  of  moisture 
from  this  dried  air  on  the  aluminum  foils ;   and  yet  the  behavior  is  such 


152 


VAPOR    NUCLEI    AND    IONS. 


as  if  a  moisture  gradient  from  the  foil  nearest  the  sodium  to  that  more 
remote  were  permanently  maintained.  In  such  a  case  there  would  be 
slight  but  unequal  precipitation  of  vapor  on  the  two  foils,  in  an  apparatus 
passing  from  warm  to  cold,  and  persistence  would  be  due  to  freezing. 
The  only  other  explanation  is  the  possibility  of  charges  on  the  very  cold 
glass  and  on  other  insulators  which  can  not  be  earthed. 


95.  Mean  daily  ionization. — As  in  the  preceding  case,  the  observations 
were  now  averaged  for  single  days.  The  results  are  given  in  detail  in  table 
52.  If  given  in  the  charts  with  the  number  of  ions  in  thousands  per 
cubic  centimeter  laid  off  vertically,  very  little  that  is  new  may  be 
taken  from  these  figures,  and  they  are  therefore  omitted.  They  serve, 
however,  as  a  basis  for  the  monthly  ionizations  which  follow,  and  in 
comparing  the  ionizations  with  the  nucleation  of  the  atmosphere  these 
charts  are  useful.  Thus,  it  would  be  difficult  to  detect  synchronism 
in  August,  September,  October,  November,  December;  but  from  the 
middle  of  January  to  the  end  of  February  suspicions  of  this  kind  would 
be  justified. 

Table  52. — Mean  daily  ionizations  corresponding  to  table  51. 


Positive 

Negative 

Positive 

Negative 

Positive 

Negative 

Date. 

ions. 

ions. 

Date. 

ions. 

ions. 

Date. 

ions. 

ions. 

n  X  io~s 

»  X  10-8 

»Xio~3 

n  X  10-3 

nXio~s 

wxio-3 

1905. 

1905. 

1905. 

July  26 

0.90 

Aug.  28 

o.55 

o.73 

Sept.  29 

0.79 

0.72 

29 

•93 

0.85 

29 

•74 

.69 

30 

.46 

.36 

3i 

1.30 

•76 

30 

.78 

.66 

Oct.     2 

•34 

.41 

Aug.  1 

•73 

.89 

„       3I 

•75 

.82 

3 

•95 

.64 

2 

1.07 

•73 

Sept.  1 

1 .02 

•73 

4 

•54 

•  65 

3 

1.24 

.82 

2 

.62 

•49 

5 

.41 

1 .00 

4 

.66 

.76 

4 

.88 

1. 10 

6 

115 

1.66 

5 

•73 

.98 

7 

•85 

•  79 

7 

.84 

•85 

7 

1.58 

i-34 

8 

1. 3i 

i-34 

9 

2.12 

.80 

8 

.91 

•52 

9 

1. 17 

.88 

10 

•58 

1.07 

9 

1 .20 

•75 

11 

•49 

•58 

11 

.69 

1. 10 

10 

1.29 

1 .04 

12 

1.07 

•44 

12 

•79 

i-39 

11 

I. 31 

.88 

13 

•75 

•59 

13 

.42 

•99 

12 

.96 

1.05 

H 

i-45 

1. 18 

14 

1. 01 

•94 

14 

2.05 

1.85 

15 

1-34 

•94 

16 

.61 

•5i 

15 

i-59 

1.42 

16 

1.05 

.41 

17 

1. 14 

.86 

16 

1.52 

1.04 

18 

i-43 

.67 

18 

•44 

•38 

17 

152 

1.27 

19 

92 

•34 

19 

•9i 

1. 01 

18 

i-45 

1 -52 

20 

.69 

•45 

20 

1.08 

•39 

19 

1.67 

1-52 

21 

1.08 

•73 

23 

.89 

1. 21 

21 

1.29 

•93 

22 

•39 

.42 

24 

.40 

•43 

22 

.78 

.87 

23 

1.30 

1.29 

25 

.64 

•99 

23 

i-43 

1.52 

25 

1. 14 

1.65 

26 

1 .04 

1.76 

24 

•87 

.96 

26 

•95 

1 .  12 

27 

•97 

1.08 

25 

1   13 

.78 

27 

•47 

•52 

30 

•79 

1 .  12 

26 

i-45 

1. 21 

28 

1 .00 

•85 

3i 

.44 

1-39 

ATMOSPHERIC    IONS. 


153 


Table  52.— Mean  daily  ionizations  corresponding  to  table  51.— Continued. 


Positive 

Negative 

Positive 

Negative 

Positive 

Negative 

Date. 

ions. 

ions. 

Date. 

ions. 

ions. 

Date. 

ions. 

ions. 

n  X  10-8 

n  X  io~8 

n  X  io~8 

n  x  10-8 

»  X  10-8 

n  X  10-8 

1905. 

1905. 

1906. 

Nov.  1 

1 .29 

o.73 

Dec.  21 

1.26 

0.78 

Feb.  9 

0.87 

0.63 

2 

1. 12 

i-59 

1906. 

10 

•83 

59 

3 

•65 

•45 

Jan.  1 

1. 91 

.76 

11 

1.29 

•93 

4 

•35 

•38 

2 

4-51 

1. 21 

12 

136 

1. 11 

6 

1 .20 

.50 

3 

1 .60 

.70 

13 

•85 

•50 

7 

1. 01 

1. 16 

4 

.86 

•55 

H 

•59 

.28 

8 

.88 

•50 

5 

1.84 

1.77 

15 

•94 

•52 

9 

.38 

1.85 

6 

1.72 

•94 

16 

1.05 

.89 

10 

•55 

•50 

8 

2.01 

1. 14 

17 

.70 

•38 

11 

.72 

1  13 

9 

1.66 

•75 

19 

76 

•65 

13 

.60 

•97 

10 

1.78 

•23 

20 

1  13 

.60 

H 

1.65 

.91 

11 

1.83 

•55 

21 

.91 

•7i 

16 

•56 

1. 14 

12 

.89 

•55 

22 

115 

1 .00 

17 

•53 

1.05 

13 

3-15 

•75 

23 

1. 00 

•79 

18 

•76 

1.74 

15 

1. 12 

1 .00 

26 

1.24 

•97 

20 

•29 

i-35 

16 

1.03 

•47 

27 

1. 17 

•73 

21 

.64 

1.04 

17 

1. 17 

.60 

28 

1. 5i 

1. 01 

22 

.80 

i  13 

18 

•87 

.23 

Mar.  1 

1.29 

1.04 

23 

1 .00 

•3i 

19 

1.36 

•99 

2 

.81 

•75 

24 

.46 

•43 

20 

.82 

•56 

3 

•7i 

1. 57 

27 

1. 10 

•74 

22 

105 

.96 

5 

1.78 

•92 

28 

•55 

.86 

23 

1 .  11 

•47 

6 

.88 

65 

Dec.  4 

.66 

i-35 

24 

1. 41 

1.62 

7 

1.24 

.76 

5 

2.08 

1.57 

25 

i-54 

71 

8 

1.62 

•71 

6 

1.03 

•55 

26 

1.70 

.40 

10 

•95 

•47 

7 

1.76 

.76 

27 

130 

.56 

12 

1. 17 

1. 14 

8 

1. 41 

•39 

29 

2.18 

94 

13 

1. 00 

.60 

9 

1. 12 

1. 00 

30 

.83 

•95 

14 

•79 

•50 

11 

1.25 

.82 

^   3I 

i-45 

1. 17 

15 

1. 17 

1.05 

12 

1.32 

.61 

Feb,  1 

1.50 

•72 

16 

1.38 

1.09 

13 

1 .60 

1. 16 

2 

2.03 

•79 

17 

.41 

•44 

14 

•32 

79 

3 

105 

.69 

19 

105 

1.09 

15 

2.15 

79 

4 

•93 

1. 18 

20 

•57 

•73 

16 

2.41 

•57 

5 

150 

•23 

22 

.84 

.88 

18 

1. 41 

49 

6 

.83 

•37 

23 

1.32 

1. 12 

19 

1. 18 

1.58 

7 

1.03 

1.04 

24 

•47 

•47 

20 

1.07 

.81 

8 

•94 

103 

26 

1.06 

•85 

96.  Mean  monthly  ionizations  and  conclusion. — The  straightforward 
way  of  arriving  at  a  conclusion  as  to  the  presence  or  absence  of  a  relation 
between  the  nucleation  and  the  ionization  of  the  atmosphere  consists 
in  comparing  the  average  monthly  values  for  both  cases.  This  is  done 
in  table  53,  and  graphically  in  fig.  62. 

The  curve  showing  the  distribution  of  negative  ions  is  probably  the 
more  trustworthy,  as  these  observations  were  made  last.  The  positive 
distribution  curve  is  too  high  in  December  and  January  for  the  reasons 
already  stated,  and  its  more  probable  course  during  these  two  months  is 
indicated  by  the  dotted  line.    It  seems  exceedingly  curious  that  whereas 


*54 


VAPOR    NUCLEI    AND    IONS. 


the  fluctuations  of  positive  and  negative  ionization  in  successive  obser- 
vations, on  the  same  or  on  succeeding  days,  usually  show  the  same  sign, 
although  not  the  same  absolute  value,  this  is  not  in  general  the  case 
with  the  monthly  ionizations.  The  two  curves  of  fig.  62  throughout  the 
greater  part  of  their  course  vary  in  opposite  directions. 

Table  53. — Mean  monthly  ionizations, 
corresponding  to  table  51. 


Positive 

Negative 

Date. 

ions. 

ions. 

n  Xio-3 

n  Xio-3 

1905. 

Aug. 

1. 16 

1 .02 

Sept. 

•95 

.78 

Oct. 

.80 

•94 

Nov. 

•77 

.96 

Dec. 

1.38 

.88 

1906. 

Jan. 

1.58 

.80 

Feb. 

1 .09 

•73 

Mar. 

1.03 

.84 

Compared  with  the  uniform  curve  for  nucleation  the  appearance  of 
the  ionization  curve  is  sufficiently  distinctive.  One  might  perhaps  be 
inclined  to  refer  the  dip  in  the  negative  curve  between  November  and 
February  to  the  more  marked  "absorption"  of  the  negative  ions  by  the 
increasing  nucleation.  But  the  two  curves  are  not  sufficiently  similar 
and  there  is  no  reason  why  the  absorbed  ion  should  fail  to  have  a  record 
in  the  condenser.  The  only  conclusion  to  be  drawn  from  the  results 
for  the  distribution  of  either  the  positive  or  the  negative  ions  is  this, 
that  there  is  no  discernible  relation  between  the  number  of  ions  and 
the  number  of  Aitken  nuclei  present  in  the  atmosphere  at  any  time,  or 
that  the  two  distributions  result  from  entirely  distinct  causes.  The 
ionization  of  a  given  region  is  independent  of  artificial  local  contribu- 
tions, however  abundant  these  may  be. 


CHAPTER  VI. 

THE  VARIATIONS  OF  THE  COLLOIDAL   NUCLEATION   OF   DUST-FREE  AIR 

IN  THE  LAPSE  OF  TIME. 

97.  Introductory. — Above  (Chapter  I,  section  26,  et  seq.)  and  in  my 
address*  before  the  Physical  Society,  I  gave  an  account  of  observa- 
tions made  several  times  daily  since  May  9,  1905,  in  a  search  for  the 
possible  occurrence  of  an  ultra -mundane  radiation.  The  work  was 
there  summarized  as  follows: 

Using  the  most  sensitive  condensation  method,  i.  e.t  that  depending  on  the  depres- 
sion of  the  limiting  asymptote  of  non-energized,  dust-free  air,  no  change  of  the  quality 
of  scrupulously  filtered  atmospheric  air  has  thus  far  been  detected.  .  .  .  Naturally  [ions] 
would  vanish  during  the  slow  passage  of  air  through  the  filter,  but  fresh  ions  should  be 
reproduced  within  the  fog  chamber  by  the  same  agency  which  generates  them  without.  .  .  . 
Probably,  therefore,  the  coronal  method  is  as  yet  inadequately  sensitive  to  cope  with 
variations  of  the  small  nucleations  specified. 

The  ions,  which  are  relatively  large  nuclei,  withdraw  much  of  the 
available  moisture  which  would  otherwise  be  precipitated  on  the  col- 
loidal nuclei  of  dust-free  air.  Hence  the  size  of  the  terminal  corona  is 
diminished.  The  advantage  of  the  method  is  its  independence  of  the 
drop  in  pressure  if  this  exceeds  a  certain  value. 

Since  the  discovery  announced  by  A.  Wood  and  A.  R.  Campbellf  on 
the  probability  of  cosmical  radiation  as  evidenced  by  the  existence  of  a 
daily  period  of  the  same,  showing  maximum  ionization  between  8  and 
10  a.  m.  and  10  p.  m.  and  1  a.  m.,  minimum  ionization  at  about  2  p.  m. 
and  4  A.M.,  I  have  taken  the  subject  up  again.  It  seems  possible  that  I 
overestimated  the  sensitiveness  of  the  earlier  method.  I  have  therefore 
changed  it  in  the  present  experiment,  replacing  the  large  terminal 
coronas  by  the  small  coronas  very  near  the  fog  limit. 

98.  Method  and  data. — The  observations,  in  other  words,  are  now  made 
with  a  drop  in  pressure,  but  just  sufficient  to  produce  coronal  condensa- 
tion on  the  larger  colloidal  nuclei  of  dust-free  air  (dp  =  21  cm.).  The 
sizes  of  coronas  vary  rapidly  with  the  pressure  difference  and  hence  with 
the  barometer,  p,  etc.,  and  great  care  must  be  taken  with  these  details. 
This,  however,  has  been  done  and  the  results  obtained  are  given  in  table 
54  and  in  the  chart  (fig.  64). 

*  Physical  Review,  xxn,  p.  105,  1905;  also  p.  109,  on  Radiant  fields. 
t  Nature,  vol.  73,  p.  583,  1906. 

155 


156 


VAPOR    NUCLfcl    AND    IONS. 


The  table  gives  the  angular  diameter  (s)  of  the  successive  coronas, 
and  other  data  to  be  presently  explained,  from  which  the  number  of 
nuclei  (n)  per  cubic  centimeter  may  be  obtained.     Observations  were 

Table  54- — Colloidal  nucleation  (s)  of  dust-free  air  near  the  fog  limit  in  their  time 
variations,  observed  two  or  more  times  daily,  dp  =  27  cm.  (observed  at  fog  chamber, 
isothermally)  =  p-pz.     Computed  dp  =/> - p2  =  2 1  cm. 


Date. 

Time. 

P-Pz> 

J. 

P. 

J-1. 

n  X  io-s. 

1906. 

h.     m. 

May   21 

9  30 

27.4 

3-6 

76.4 

3-2 

9-7 

12   0 

26 

•7 

2. 1 

2.8 

6.1 

5  30 

27 

•3 

30 

•3 

2.7 

5-9 

22 

9  15 

.  1 

2.9 

•7 

3-1 

8-5 

3  00 

3 

3-1 

.6 

30 

7-7 

23 

9  15 

•3 

29 

•4 

2.7 

6.1 

3  15 

•5 

4.4 

.  1 

3-7 

16 

24 

9  30 

.0 

2.8 

.0 

2.8 

6-3 

4  00 

.  1 

3-5 

75 

.8 

3-2 

97 

25 

9  00 

.2 

4-3 

.6 

3-8 

18 

26 

8  50 

•4 

4-9 

•4 

4.0 

19 

3  10 

.  2 

4-9 

•3 

4-2 

22 

27 

10  25 

.  1 

4-2 

.2 

3-6 

15 

4  25 

.  1 

4-9 

.0 

4.2 

22 

28 

9   5 

27 

•3 

5-2 

75 

.0 

4.2 

22 

3  45 

.  1 

5-4 

74 

•9 

4.6 

30 

29 

11  00 

.  1 

4-9 

75 

.  1 

4.2 

22 

3  50 

.  1 

4-9 

.2 

4-3 

25 

30 

8  50 

.  1 

2.9 

•9 

2.7 

6 

3  10 

•3 

3-9 

.8 

3-3 

11 

3i 

9  30 

0 

3-o 

•9 

29 

7 

2  45 

0 

4-5 

6 

4-3 

25 

June   1 

9  30 

2 

3-9 

7 

34 

12 

2  45 

26 

9 

3  9 

3-9 

17 

2 

9   5 

27 

0 

3-7 

6 

3-5 

13 

2  45 

1 

3-7 

6 

3-3 

11 

3 

10  00 

3 

4.9 

9 

4-4 

26 

4  30 

2 

4.2 

9 

3-8 

18 

4 

8  30 

27 

1 

3-i 

76 

4 

30 

8 

3  35 

3 

4-3 

2 

4.0 

19 

5 

9  20 

1 

3-9 

75 

9 

3-7 

16 

3  20 

1 

4-2 

6 

3-8 

18 

6 

10   6 

1 

50 

1 

4-3 

24 

3  20 

2 

59 

74 

8 

4-9 

37 

7 

9  10 

3 

4-9 

75 

6 

4.2 

22 

3  45 

3 

4.8 

9 

4-3 

25 

8 

9  25 

1 

3-6 

76 

2 

3-6 

15 

2  45 

4 

4.6 

0 

4.0 

19 

9 

9  10 

3 

5-o 

75- 

5 

4-3 

25 

2  45 

26! 

9 

3-5 

0 

3-i 

8 

8  15 

27. 

3 

5-1 

1 

4.1 

20 

9  20 

3 

5-i 

3 

4.2 

22 

10 

9  55 

2 

5-1 

2 

4-3 

25 

3  15 

3 

5-6 

0 

4.6 

30 

6  15 

2 

5-1 

1 

4-3 

25 

11 

8  40 

2 

4-9 

5 

43 

25 

2  55 

1 

4.2 

6 

3-8 

18 

TIME    VARIATIONS    OF    NUCLEI. 


157 


Table  54,  continued. — Colloidal  nucleation  (s)  of  dust-free  air  near  the  fog  limit  in 
their  time  variations,  observed  two  or  more  times  daily.  dp*>*  27  cm.  (observed  at  fog 
chamber,  isothermally)  =*p-  pz.     Computed  dp  =  p  -  p2  =  2 1  cm. 


Date. 

Time. 

P-P*. 

s. 

P. 

J1. 

n  X  io-». 

1906. 

h.     m. 

June   1 1 

6   5 

O.I 

3-6 

0.8 

3-3 

11 

12 

8  45 

27.1 

3 

0 

76 

3 

3- 

0 

8 

12  00 

.2 

3 

4 

3 

3- 

3 

11 

3  00 

.0 

2 

8 

2 

2. 

9 

7 

13 

9  00 

.  1 

2 

5 

7 

2 

7 

6 

11  40 

.  1 

2 

5 

7 

2 

7 

6 

2  35 

.2 

3 

0 

6 

3 

0 

8 

6   5 

.2 

3 

5 

5 

3 

5 

13 

H 

9  35 

.2 

3 

9 

2 

3 

7 

16 

12  20 

.0 

2 

9 

0 

2 

9 

7 

3  30 

.2 

4 

0 

75 

8 

3 

6 

15 

6  10 

.  1 

3 

7 

7 

3 

4 

12 

15 

9  20 

.  1 

4 

2 

7 

3 

9 

18 

12  00 

.2 

4 

2 

7 

3 

7 

16 

2  40 

.  1 

4 

5 

7 

4 

2 

22 

6  00 

.  1 

3 

6 

8 

3 

3 

11 

16 

9  50 

■4 

4 

7 

9 

4 

1 

21 

3  45 

.2 

4 

1 

3 

7 

16 

17 

10  00 

.  1 

4 

0 

6 

3 

6 

15 

12  00 

•3 

5 

3 

6 

4 

6 

30 

3  25 

•3 

5 

1 

6 

4 

5 

28 

6  10 

26.8 

2 

8 

7 

3 

0 

8 

18 

9  15 

27.1 

3 

0 

76 

0 

2 

9 

7 

12  35 

.0 

3 

0 

75 

9 

2 

9 

7 

3  00 

.2 

3 

9 

9 

3 

5 

13 

6  00 

.2 

3 

8 

8 

3 

4 

12 

19 

11  00 

.1 

3 

5 

6 

3 

1 

8 

12  55 

.2 

4 

4 

6 

3 

8 

18 

3  40 

.2 

4 

6 

6 

4 

0 

19 

20 

5  35 

.  1 

4 

1 

7 

3 

8 

18 

21 

10  15 

•  3 

4 

0 

8 

3 

.6 

14 

1  00 

.1 

3 

8 

7 

3 

•5 

13 

3  10 

.  1 

3 

7 

6 

3 

3 

11 

6  20 

.  1 

3 

8 

3 

•4 

12 

22 

9  15 

.  1 

4 

4 

•3 

3 

.8 

18 

12  10 

.  1 

4 

2 

•3 

3 

.6 

15 

2  50 

.2 

5 

5 

.2 

4 

•7 

33 

6  10 

.2 

5 

3 

4 

•5 

28 

made  at  about  9  a.  m.  and  3  p.  m.,  as  near  the  time  of  the  Wood  and 
Campbell  maxima  and  minima  as  my  duties  permitted,  on  the  successive 
days  and  hours  given  by  the  abscissas. 


99.  Deductions. — Figure  64  shows  in  the  first  place  that,  in  general, 
minima  and  maxima  of  nucleation  would  have  to  appear  at  about  the 
time   at  which  Wood   and   Campbell  observed  maxima  and  minima, 


i58 


VAPOR    NUCLEI    AND    IONS. 


an  explanation  on  similar  lines  to  the 


respectively ;  or  that  an 
inversion  of  Wood  and 
Campbell's  results  is  a 
question,  since  there  is 
usually  incremented  nu- 
cleation  in  the  afternoon 
as  compared  with  the 
morning.  This,  however, 
may  be  explained,  if  the 
ions  are  large,  even  in 
comparison  with  the 
larger  gradations  of  col- 
loidal nuclei.  Fewer  of 
these  will  therefore  be 
captured  in  proportion 
as  the  ionization  is 
larger.  Hence  the  figure 
shows  at  a  an  apparent 
corroboration  of  Wood 
and  Campbell's  results; 
at  e  an  omission  or  in- 
version of  the  periods. 
But  the  e's  are  much 
fewer  in  number,  and  in 
comparison  with  the  am- 
plitude of  the  a 's,  the  e  's 
are  frequently  neutral. 

In  the  second  place, 
the  high  nucleation  dur- 
ing the  period  of  rain  is 
noteworthy.  Here,  then, 
few  ions  were  present. 
As  there  is  a  modification 
of  the  atmospheric  po- 
tential gradient  during 
this  time ,  one  might  favor 
ideas  suggested  by  Richardson.* 


100.  Effect  of  the  barometer. — In  the  further  development  of  the 
investigation  on  the  time  variations  of  the  efficient  colloidal  nucleation  in 
filtered  air,  the  results  are  of  the  same  character  as  those  already  dis- 


*  Nature,  lxxiii,  p.  607,  1906. 


TIME    VARIATIONS    OF    NUCLEI.  1 59 

cussed;  but  the  dependence  of  the  nucleation  on  the  fluctuations  of  the 
barometer  now  shows  itself  even  more  obtrusively  than  before.  The 
minima  of  atmospheric  pressure  coincide  with  maxima  of  colloidal 
nucleation,  and  therefore  (by  inference  but  not  necessarily)  with  minima 
of  ionization  of  the  dust-free  air,  both  in  the  daily  and  in  the  weekly 
periods  of  observation.  Maximum  pressure,  therefore,  would  correspond 
to  maximum  ionization  as  if  the  radiant  energy  originated  in  the  com- 
pression of  the  atmosphere,  or  were  dependent  on  the  mass  of  the  atmos- 
phere bearing  on  a  given  place.  This  would,  if  finally  substantiated,  be 
an  important  inference,  but  no  more  so  than  the  more  direct  correlative 
result  that  minimum  pressure  and  maximum  colloidal  nucleation  of  dust- 
free  air  go  together. 

At  the  same  time,  since  the  change  of  absolute  temperature  (r)  due 
to  a  sudden  expansion  equivalent  to  a  drop  (dp)  at  a  barometric  pressure 
(p)  and  vapor  pressure  (7:)  may  be  written 

the  correction  for  the  changes  of  the  barometer  are  in  the  same  sense  as 
the  observed  changes  in  nucleation.  These  corrections  are  found  by 
varying  the  numerator  of  dpj(p-Tt)  and  observing  the  effect  on  the 
angular  diameter  of  the  corona.  While  I  can  see  no  room  for  error,  it 
must  nevertheless  be  acknowledged  that  the  present  method  of  small 
exhaustion,  though  possibly  more  sensitive,  is  not  as  straightforward 
as  the  method  mentioned  in  my  address,  where  no  variation  could  be 
detected,  the  terminal  corona  remaining  unchanged. 

At  the  present  stage  of  investigation,  therefore,  the  need  of  any 
external  radiation  has  ceased  to  be  obvious;  and  the  results,  if  they 
exceed  the  barometer  correction,  are  most  directly  referable  to  changes 
of  pressure  within  the  gas,  the  number  of  colloidal  nuclei  being  greatest 
when  the  pressure  is  least. 

101.  Corrections. — In  table  54  and  the  following  table  55,  p  is  the 
barometric  pressure ;  p3  the  final  pressure  when  fog  chamber  and  vacuum 
chamber  are  in  communication;  p2  the  (computed)  pressure  which  would 
be  observed  in  the  fog  chamber  if  it  could  be  instantly  separated  from 
the  vacuum  chamber  after  exhaustion.  Hence  the  true  drop  in  pressure 
is  dp  =p  -  p2  while  dp  =  p  -  p3  is  observed.  The  initial  pressure  (p)  differs 
from  the  atmospheric  pressure  by  a  few  millimeters,  due  to  the  leakage 
of  the  4-inch  stopcock  from  fog  chamber  to  vacuum  chamber.  As  it  is 
impossible  to  retain  the  same  value  of  p  and  dp  throughout,  a  correction 
must  be  applied,  seeing  that  the  adiabatic  cooling  is  given  by  t2/t1  = 
(1  -dp/(p-  7r))(*~c)/*,  where  n  is  the  vapor  pressure  of  water.    By  varying 


l6o  VAPOR    NUCLEI    AND    IONS. 

dp  from  26  to  28  cm.  and  observing  the  changes  of  s  (angular  coronal 
diameter)  when  p  is  constant,  a  table  was  investigated  from  which 
reductions  could  at  once  be  made  to  dp  =  27  cm.  and  £  =  76  cm.;  for 
instance, 


dp  -26.8 

cm. 

ds- 

=  +0.34 

P 

=  75.8 

ds- 

=  -O.I  I 

26.9 

+    .17 

75-9 

-    .06 

27.0 

+    .00 

76.0 

+    .00 

27.1 

-    .15 

76.1 

+  .06 

27.2 

-    .30 

76.2 

+  .11 

The  value  of  s  corrected  for  both  pressures  is  given  in  this  table. 

In  the  same  way  the  case  of  apparatus  II  (to  be  described  presently) 
was  treated,  the  reductions  being  much  larger  here.  Thus  the  data 
(barometer,  75.5;   temperature,  21.40  C.) 

dp 


24.9 

J-1.7 

dp  =25.6 

s  -3.1 

25.6 

3.6 

26.2 

5.2 

264 

5.6 

25.6 

2.9 

24.8 

1  wo 

were  consecutively  observed,  showing  that  the  coronas  after  long  waiting 
are  much  larger  than  when  obtained  in  succession.  The  efficient  nuclea- 
tion  of  the  fog  chamber  increases  in  the  lapse  of  time,  probably  from  the 
evanescence  of  water  nuclei  associated  even  with  small  coronas.  From 
these  results  corrections  of  the  form 

dp 


25.5 

ds=*  +0.27 

£=75.9 

ds  —  0.08 

25.6 

+    .00 

76.0 

+   .00 

25.7 

-f    .27 

76.1 

+    .08 

were  made  out.  These  examples  show  how  critically  important  these 
corrections  are,  and  how  difficult  it  will  be  to  decide  whether  anything 
more  than  the  barometer  fluctuation  is  being  observed. 

102.  Further  data. — It  follows  from  section  101  that  there  would  be  a 
chance  for  error  in  the  unavoidable  leakage  of  the  stopcock,  and  the 
best  method  of  coming  to  a  decision  would  consist  in  the  installation  of  a 
second  fog  chamber,  side  by  side  with  the  other,  but  containing  a  smaller 
exhaust  pipe  (2  inches  in  diameter,  18  inches  long)  and  therefore  a  more 
perfect  stopcock. 

Fig.  65  shows  two  fog  chambers  (F  and  Ff)  and  appurtenances  in  place, 
each  with  an  independent  vacuum  chamber  (V  and  V)  and  goniometer. 
Other  parts  will  be  easily  recognized. 

Table  55  and  chart  66  contain  the  new  data,  the  old  fog  chamber 
(4-inch  cock)  being  marked  I,  the  new  fog  chamber  (2-inch  cock), marked 
II.    The  latter  was  first  tested  at  different  values  of  dp,  and  dp  =  25. 6 


TIME    VARIATIONS    OF    NUCLEI. 


161 


NMIHNN^d 

fH 

IPS 

II 

13 

>    1  i  '   ~ 

■y 

L 

I   i  l  i 

-1 

Dfliirw 

ti.i  jri  ;'  i 

i  ill  III'' JL 

1     ' 

pi 

IF; 

Or 

ii1 

MB       •  ■  "Mi     t;'/ 

c 

Fig.  65.— Independent  fog  chambers  with  2-inch  and  4-inch  efflux  side  by  side. 
Vacuum  chambers,  V  and  V ;  fog  chambers,  F  and  F'. 


finally  selected.  At  the  outset  the  values  of  s  may  be  uncertain,  because 
of  internal  sources  of  nucleation  and  similar  difficulties. 

Four  observations  were  usually  made  daily.  Data  corresponding  to 
I  and  II  are  distinguished  by  subscripts,  and  those  of  II  were  usually 
observed  about  five  minutes  after  the  time  given  for  I.  One  may  note 
the  much  greater  efficiency  of  the  apparatus  with  2-inch  pipes  as  com- 
pared with  the  other  with  4-inch  pipes,  the  reason  for  which  is  not  easily 
seen.  As  a  whole  the  observations  for  apparatus  I  during  the  end  of 
June  and  the  beginning  of  July  run  parallel  to  the  barometric  decrement, 
and  the  astonishingly  high  values  on  June  29  and  30  occur  during  a  period 

Table  55.— Colloidal  nucleations  near  the  fog  limit  in  their  time  variations.  Fog  cham- 
ber I  with  4-inch  exhaust  pipes;  3p=p-  £3=27  cm.;  II  with  2-inch  exhaust  pipes; 
dp  =p  -  ps  -  25.6  cm.;  p  - p2  =  21  cm.  and  20  cm.,  respectively. 


Date. 

Time. 

*Pi-lhh 

*v         P 

«V 

n  X  10-3 

8P*-P-P* 

•y2. 

«v 

n2  X 
10-8. 

h.      m. 

June  23 

9     15 

27.1 

4-3    75 

5 

3.8 

18 

'27.6 

7-3 

6.4 

75 

12     35 

.  1 

4 

5 

6 

4 

1 

20 

4 

7 

7 

7-4 

86 

3     15 

.  2 

4 

6 

6 

4 

1 

20 

4 

7 

3 

7.0 

82 

5     50 

.0 

3 

6 

6 

3 

4 

12 

3 

7 

1 

7.0 

82 

24 

10     20 

.  1 

3 

8 

s 

3 

5 

13 

2 

7 

5 

7-9 

93 

12     50 

.0 

4 

1 

7 

3 

9 

18 

226 

5 

5 

2 

5-o 

3« 

4     15 

.  1 

3 

9 

7 

3 

6 

15 

6 

5 

1 

4.6 

30 

6     20 

.  1 

4 

3 

7 

4 

O 

19 

5 

5 

5 

5-3 

45 

25 

9     10 

.2 

5 

1 

7 

4 

6 

30 

5 

6 

0 

5-8 

57 

12     10 

.  1 

4.0 

s 

3 

7 

16 

•5 

4 

9 

4-7 

32 

Early  results. 


*  Results  in  succession. 


l62 


VAPOR    NUCLEI    AND    IONS. 
Table  55. — Continued. 


Date. 

Time. 

tpi-P-h 

j. 

A- 

/«. 

rcx  io-3 

dp2=p-p3 

*,. 

•V 

n2x 

IO~8. 

h. 

w. 

June  25 

3 

35 

27.1 

4.2 

75-8 

3-9 

18 

26.5 

5-o 

4.8 

34 

6 

10 

.  1 

3 

0 

7 

2 

7 

6 

•5 

5 

3 

5 

1 

40 

26 

9 

30 

27.1 

4 

0 

76 

0 

3 

9 

17 

12 

20 

.  1 

4 

1 

75 

9 

3 

9 

17 

26.5 

4 

9 

4 

8 

34 

12 

35 

9 

25.6 

2 

1 

2 

0 

2 

2 

40 

27.  2 

5 

1 

9 

3 

7 

io 

.6 

2 

6 

2 

5 

4 

5 

30 

.2 

4 

7 

9 

4 

3 

25 

.6 

2 

6 

2 

5 

4 

27 

9 

10 

.  2 

4 

9 

B 

4 

5 

28 

.6 

2 

7 

2 

5 

4 

12 

25 

.  1 

4 

9 

7 

4 

6 

32 

.6 

2 

7 

2 

5 

4 

3 

00 

.  1 

4 

1 

6 

3 

7 

16 

.6 

3 

5 

3 

2 

9 

6 

5 

.2 

4 

8 

6 

4 

2 

22 

•5 

3 

5 

3 

4 

11 

28 

9 

5 

•3 

5 

7 

9 

5 

2 

43 

.6 

3 

0 

3 

0 

7 

12 

5 

.  1 

4 

9 

9 

4 

7 

33 

•5 

3 

0 

3 

2 

9 

3 

30 

.2 

5 

1 

8 

4 

7 

33 

•5 

2 

8 

2 

6 

5 

29 

9 

00 

.  1 

5 

0 

3 

4 

5 

28 

•7 

3 

7 

2 

9 

7 

12 

30 

■5 

7 

0 

2 

5 

8 

59 

.6 

3 

8 

3 

3 

10 

12 

40 

.2 

5 

1 

2 

4 

3 

25 

2 

55 

.2 

5 

4 

2 

4 

6 

30 

25. 6 

3 

7 

3 

2 

9 

6 

00 

.  2 

9 

0 

2 

4 

2 

22 

*  .6 

3 

8 

3 

2 

9 

30 

9 

25 

•  5 

7 

0 

2 

5 

8 

59 

•7 

4 

4 

3 

6 

14 

12 

30 

•  1 

3 

3 

1 

4 

6 

30 

.6 

3 

2 

2 

6 

5 

3 

5 

.  1 

5 

3 

2 

4 

7 

33 

.6 

4 

0 

3 

3 

10 

5 

50 

.  1 

5 

3 

3 

4 

7 

33 

.6 

4 

3 

3 

7 

16 

July  1 

10 

00 

27.2 

5 

1 

75 

6 

4 

6 

30 

25.6 

3 

3 

3 

0 

7 

12 

10 

.  1 

4 

5 

6 

4 

1 

20 

.6 

3 

2 

2 

9 

7 

1 

45 

.  1 

4 

1 

6 

3 

7 

43 

•7 

3 

6 

2 

9 

7 

6 

25 

.2 

5 

2 

6 

4 

7 

33 

•5 

2 

9 

2 

9 

7 

2 

9 

15 

•4 

S 

7 

6 

4 

9 

37 

.6 

3 

6 

3 

3 

10 

12 

30 

.  1 

4 

6 

6 

4 

2 

22 

.6 

3 

6 

3 

3 

10 

2 

20 

•3 

5 

3 

5 

4 

8 

36 

.6 

4 

2 

3 

8 

17 

6 

00 

.  2 

5 

5 

5 

4 

9 

37 

.6 

3 

7 

3 

3 

10 

3 

9 

40 

•3 

5 

6 

5 

4 

9 

37 

.6 

3 

8 

3 

4 

1 1 

12 

30 

.  2 

5 

3 

5 

4 

7 

33 

.6 

3 

5 

3 

1 

9 

2 

00 

•3 

5 

3 

4 

6 

30 

.6 

3 

6 

3 

2 

9 

6 

50 

.  2 

5 

3 

5 

4 

6 

30 

.6 

3 

9 

3 

5 

13 

4 

9 

15 

.  2 

5 

3 

2 

4 

5 

28 

.6 

4 

1 

3 

5 

13 

12 

00 

.  1 

5 

0 

4 

4 

26 

•7 

4 

4 

3 

5 

13 

4 

50 

.  2 

5 

2 

3 

4 

5 

28 

.6 

4 

3 

3 

7 

16 

6 

5 

•3 

5 

2 

5 

4 

5 

28 

.6 

3 

5 

3 

1 

8 

5 

8 

55 

.  2 

4 

0 

76 

5 

3 

9 

18 

.6 

2 

8 

3 

2 

9 

12 

10 

•4 

4 

7 

5 

4 

4 

27 

2 

45 

.2 

3 

7 

5 

3 

7 

16 

.6 

2 

I 

3 

6 

14 

6 

20 

.  2 

3 

3 

7 

3 

4 

12 

.6 

1 

9 

2 

4 

4 

6 

9 

50 

27.  2 

3 

7 

77 

1 

4 

0 

19 

256 

1 

9 

2 

8 

6 

12 

35 

.  1 

2 

7 

0 

3 

1 

9 

.6 

1 

8 

2 

6 

5 

12 

45 

_  2 

2 

9 

0 

3 

1 

8 

3 

15 

t  2 

3 

3 

76 

9 

3 

5 

13 

25.6 

1 

9 

2 

6 

5 

6 

10 

•3 

3 

8 

9 

3 

9 

19 

.6 

1 

5 

2 

2 

3 

7 

9 

20 

.  2 

3 

6 

7 

3 

6 

15 

.6 

2 

5 

3 

1 

8 

2 

25 

_  2 

4 

2 

4 

2 

22 

.0 

1 

3 

3 

6 

H 

7 

45 

.  2 

3 

7 

76 

4 

3 

5 

14 

.6 

3 

S 

3 

8 

17 

8 

8 

50 

.  2 

4 

2 

2 

3 

9 

18 

•4 

2 

8 

3 

5 

13 

9 

00 

.  2 

3 

8 

.2 

3 

6 

l5 

2 

55 

.  2 

4 

3 

.  1 

4 

0 

20 

!6 

2 

7 

2 

8 

6 

5 

40 

•3 

4.9 

.0 

4-4 

27 

.6 

3-o 

3-o 

7 

TIME    VARIATIONS    OF    NUCLEI. 


>63 


Table  55.— Continued. 


Date. 

Time. 

dpx-p-p* 

jfc. 

P- 

#v 

»X  lO~3dp2  = 

M>3 

J2. 

j'2. 

n2x 

IO-'. 

h.     m. 

July     9 

9     00 

27.  2 

5-2 

75-8 

4.8 

35             25 

4 

3  3 

3-5 

13 

2     30 

.2 

5 

1 

7 

4 

6 

30 

6 

4.1 

3 

7 

16 

5     50 

.2 

4 

8 

6 

4 

3 

25 

6 

4>l 

3 

8 

17 

10 

9     05 

.  2 

5 

2 

6 

4 

7 

33 

7 

4.0 

3 

4 

11 

2     45 

•4 

5 

7 

5 

4 

8 

35 

6 

4.0 

3 

6 

14 

5     45 

.  2 

5 

0 

4 

5 

29 

4 

2.8 

3 

0 

7 

11 

9     05 

.  2 

4 

6 

76 

2 

4 

4 

27 

5 

2.6 

3 

O 

7 

2     15 

.  2 

3 

9 

2 

3 

7 

16 

5     20 

.  2 

3-9 

.  2 

3-7 

16 

June  23 


Fig.  66.— Data  of  fig.  64  continued  for  apparatus  I  (fog  chamber  with  4-inch  pipes) 
and  apparatus  II  (fog  chamber  with  2-inch  pipes),  adjusted  for  different  exhaus- 
tions {dp  =27.3  and  25.6  cm.,  respectively).    Table  55. 

of  exceptionally  low  barometer.    The  daily  details  of  the  barometer  arc 
not  as  a  rule  reproduced. 

In  case  of  apparatus  II,  if  the  initial  observations  ^  =  27.4  be  over- 
looked, the  data  for  dp  =  26.5  are  not  unlike  magnified  parts  of  the 
corresponding  curve  for  apparatus  I.  The  chief  observations  for  appa- 
ratus II  in  June  (^  =  25.6    or  computed  dp  =20  just  above  the  fog 


164  VAPOR    NUCLEI    AND    IONS. 

limit)  do  not  in  their  details,  it  is  true,  agree  with  the  curves  for  appa- 
ratus I,  except  to  some  degree  on  June  29  and  30.  As  a  whole,  how 
ever,  they  also  strikingly  follow  the  march  of  the  decrement  of  the 
barometer.  One  may  note,  moreover,  that  it  is  not  necessary  that  the 
curves  for  apparatus  I  and  II  should  quite  agree.  If,  for  instance,  the 
preponderating  nuclei  in  the  former  case  are  colloidal,  and  in  the  latter 
case  ions,  one  should  expect  an  inverse  curve;  for  the  ions  in  I  would 
decrease  the  number  of  efficient  nuclei,  whereas  in  II  they  would  increase 
their  number.     Decision  must  be  deferred  for  further  observation. 

In  July  the  two  fog  chambers  again  fail  to  agree  in  their  daily  fluctua- 
tions, but  both  nevertheless  follow  the  barometer  closely,  in  their  broader 
variations.  The  different  sizes  of  coronas  imply  different  ratios  of  ions 
and  colloidal  nuclei,  and  hence  detailed  agreement  should  not  be  antici- 
pated. On  July  12  the  fog  chambers  were  subjected  to  modifications 
and  it  was  therefore  concluded  to  terminate  the  preliminary  series  of 
observations  at  that  point,  reserving  further  record  and  comment  for  a 
subsequent  report. 

103.  Conclusion. — It  appears,  therefore,  at  the  present  stage  of  progress 
of  the  investigation  on  the  time  variation  of  the  number  of  larger  colloidal 
nuclei  in  dust-free  wet  air,  that  the  meaning  of  the  above  results  is  not 
quite  clear.  The  probable  occurrence  of  an  effect  due  to  anything  like 
cosmical  radiation  may,  however,  be  regarded  as  excluded.  The  nuclea- 
tion  curves  vary  in  their  broad  contours  with  the  barometer,  being  a 
maximum  when  the  atmospheric  pressure  is  least.  Nevertheless  the  two 
fog  chambers  do  not,  in  their  detailed  variation,  show  appreciable 
accordance;  rather  the  reverse  of  this,  and  yet  such  a  result  may  be  due 
to  differences  in  the  ratios  of  nuclei  and  ions  entrapped  in  the  differently 
adjusted  chambers.  No.  II  in  the  above  work  (Chapter  II,  section  53) 
shows  apparent  excess  in  the  region  of  ions  as  compared  with  No.  I. 
As  a  whole  the  data  for  the  time  variation  can  not  be  regarded  as  quite 
trustworthy,  since  the  correction  to  be  added  for  variation  of  baro- 
metric pressure  and  the  drop  of  pressure  are  in  the  same  sense  as  the 
residual  effect  observed.  If  some  obscure  factor  in  the  make-up  of  these 
corrections  has  been  overlooked,  the  results  may  possibly  be  attributed 
to  it. 

From  another  point  of  view  adequate  explanation  is  now  at  hand, 
why  in  the  above  investigations  it  was  found  impossible  to  secure  rea- 
sonably coincident  results  in  the  case  of  those  groups  of  nuclei  which 
lie  in  the  region  of  the  larger  colloidal  nuclei  and  of  the  ions ;  and  it  is 
chiefly  for  this  reason  that  the  results  of  this  chapter  are  included  in  the 
present  report. 


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